Force sensor

ABSTRACT

A capacitive force sensor that is inexpensive but highly sensitive, and is hardly affected by temperature changes and in-phase noise in the use environment. A force sensor includes: a deformable body having a force receiving portion and a fixed portion; a displacement body that is connected to the deformable body, and is displaced by elastic deformation caused in the deformable body; and a detection circuit that detects an applied force, in accordance with the displacement caused in the displacement body.

CROSS REFERENCE TO THE RELATED APPLICATION

This application is a continuation of, and claims the benefit of, U.S.patent application Ser. No. 15/926,819 filed Mar. 20, 2018, which claimspriority to Japanese Patent Application No. 2017-185184 filed Sep. 26,2017, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a force sensor, and more particularly,to a sensor having a function of outputting a force acting in apredetermined axis direction and a torque acting around a predeterminedrotation axis as electric signals.

BACKGROUND ART

A conventional force sensor having a function of outputting a forceacting in a predetermined axis direction and a torque acting around apredetermined rotation axis as electric signals is a capacitive forcesensor that detects a force and a torque in accordance with changes inthe capacitance values of capacitive elements, or a strain-gauge forcesensor that detects a force and a torque in accordance with changes inthe electric resistance value of a stain gauge. Such force sensors havebeen produced on a commercial basis.

A strain-gauge force sensor requires the step of attaching a straingauge to a flexure element in the sensor manufacturing process. Thiscomplicates the assembling of the sensor. Furthermore, it is extremelydifficult for a strain-gauge force sensor to contain a stopper mechanismfor preventing sensor failures due to overload, and therefore, the useof such a stain-gauge force sensor is limited.

On the other hand, a capacitive force sensor has a simple sensorstructure, and it is easy for a capacitive force sensor to contain astopper mechanism for preventing sensor failures due to overload.Furthermore, a capacitive element is formed with two sets of parallelplates, and accordingly, an inexpensive force sensor can be obtained.Because of these features, capacitive force sensors are widely availableon markets.

However, a capacitive force sensor detects a force in the Z-axisdirection, in accordance with the sum of the capacitance values ofcapacitive elements. For example, such a detection method is illustratedin FIGS. 6 and 7 of Patent Document 1 filed by the applicant. In thiscase, the output of the sensor fluctuates due to temperature changes inthe use environment, and is further affected by in-phase noise. It is ofcourse possible to solve these problems by changing the detectioncircuit. However, this leads to higher force sensor production costs,which is undesirable.

CITATION LIST Patent Literature

Patent Literature 1: JP 2841240 B1

SUMMARY OF INVENTION Technical Problem

The present invention has been made in view of the above problems. Thatis, an object of the present invention is to provide a capacitive forcesensor that is inexpensive but highly sensitive, and is hardly affectedby temperature changes and in-phase noise in the use environment.

Solution to Problem

A first mode of a force sensor according to the present inventionincludes:

a deformable body that includes a force receiving portion and a fixedportion, and is elastically deformed by a force acting on the forcereceiving portion;

a displacement body that is connected to the deformable body, and isdisplaced by elastic deformation caused in the deformable body; and

a detection circuit that detects an applied force, in accordance with adisplacement caused in the displacement body,

wherein the deformable body includes:

a tilting portion that has a longitudinal direction and is disposedbetween the force receiving portion and the fixed portion;

a first deformable portion that connects the force receiving portion andthe tilting portion; and

a second deformable portion that connects the fixed portion and thetilting portion,

the first deformable portion extends in a direction intersecting withthe longitudinal direction on one side of the tilting portion,

the second deformable portion extends in a direction intersecting withthe longitudinal direction on the other side of the tilting portion,

the connecting portion between the first deformable portion and thetilting portion, and the connecting portion between the seconddeformable portion and the tilting portion differ in position in thelongitudinal direction of the tilting portion,

the displacement body includes a displacement portion that is connectedto the tilting portion and is at a distance from the fixed portion, thedisplacement portion being displaced by a tilting movement of thetilting portion, and

the detection circuit includes a capacitive element disposed at thedisplacement portion, and detects an applied force in accordance with achange in the capacitance value of the capacitive element.

With such a configuration, the displacement caused in the tiltingportion can be easily amplified by the action of the displacementportion that is displaced by the tilting movement of the tiltingportion. Further, if a plurality of capacitive elements are provided inthe displacement portion, it is possible to detect an applied force froma difference between the changes in the capacitance values of thecapacitive elements. That is, according to the present invention, it ispossible to provide a force sensor that is inexpensive but highlysensitive, and is hardly affected by temperature changes and in-phasenoise in the use environment.

The above force sensor may further include

a support that is disposed to face the displacement body, and does notmove relative to the fixed portion,

wherein the capacitive element may include a displacement electrodedisposed at the displacement portion of the displacement body, and afixed electrode disposed on the support to face the displacementelectrode.

In this case, the capacitive element can be stably positioned.

The displacement body may include a beam that extends in a directionintersecting with the longitudinal direction of the tilting portion. Inthis case, it is possible to effectively amplify the tilting movementcaused in the tilting portion.

The displacement portion of the displacement body may include a firstdisplacement portion and a second displacement portion defined atdifferent positions from each other on the beam, and

the detection circuit may include a first capacitive element disposed atthe first displacement portion and a second capacitive element disposedat the second displacement portion, and detect an applied force inaccordance with changes in capacitance values of the respectivecapacitive elements.

In this case, it is possible to detect an applied force from adifference between changes in the capacitance values of the capacitiveelements. Thus, a force sensor that is hardly affected by temperaturechanges and in-phase noise in the use environment can be provided.

The displacement body may include a connecting body that connects thetilting portion of the deformable body and the beam, and

the first displacement portion and the second displacement portion ofthe displacement body may be disposed on the beam symmetrically withrespect to the connecting portion between the connecting body and thebeam.

In this case, if the displacement of the tilting portion in thelongitudinal direction can be ignored, the displacement caused in thefirst displacement portion and the displacement caused in the seconddisplacement portion are of the same magnitude but have different signsfrom each other. Thus, the applied force can be detected through asimple calculation.

In the displacement body, the displacement caused in the tilting portionand the displacement caused in one of the first displacement portion andthe second displacement portion when a force in a particular directionacts on the force receiving portion may be in the opposite directionsfrom each other and be of the same size, to prevent the one of thedisplacement portions from being displaced. In this case, the appliedforce can be detected through a simple calculation.

The longitudinal direction of the tilting portion of the deformable bodymay extend in a direction intersecting with the X-axis and the Y-axis inan X-Y-Z three-dimensional coordinate system,

the beam of the displacement body may extend parallel to the X-axis, and

the detection circuit may detect at least one of an applied force in theX-axis direction and an applied force in the Z-axis direction, inaccordance with a change in the capacitance value of the capacitiveelement.

In this case, the electrode forming the capacitive element can bedisposed parallel to the X-Y plane, and thus, a force sensor can beformed with a simple structure.

The force sensor may further include

a support that is disposed to face the beam of the displacement body,and does not move relative to the fixed portion,

wherein the first capacitive element may include a first displacementelectrode disposed at the first displacement portion of the displacementbody, and a first fixed electrode disposed on the support to face thefirst displacement electrode, and

the second capacitive element may include a second displacementelectrode disposed at the second displacement portion of thedisplacement body, and a second fixed electrode disposed on the supportto face the second displacement electrode.

In this case, it is possible to stabilize the changes in the capacitancevalues of the respective capacitive elements.

The force sensor may further include:

a force receiving body that is connected to the force receiving portionof the deformable body, and receives an applied force; and

a fixed body connected to the fixed portion of the deformable body,

wherein the fixed body may be connected to the support.

In this case, it is possible to transmit the applied force to thedeformable body without fail.

The first displacement electrode and the second displacement electrode,or the first fixed electrode and the second fixed electrode may beformed with a common electrode. In this case, it is also possible todetect the applied force without fail.

A second mode of a force sensor according to the present inventionincludes:

a deformable body that is a closed-loop deformable body, the deformablebody including: two force receiving portions; two fixed portionsarranged together with the two force receiving portions alternatelyalong a closed-loop path; and four deformable portions that connect theforce receiving portions and the fixed portions adjacent to one anotheralong the closed-loop path, and are elastically deformed by one of aforce and a moment acting on the force receiving portions;

four displacement bodies that are connected to the respective deformableportions, and are displaced by elastic deformation caused in thedeformable portions; and

a detection circuit that detects at least one of an applied force and anapplied moment, in accordance with displacements caused in the fourdisplacement bodies,

wherein the tour deformable portions each include:

a tilting portion that has a longitudinal direction and is disposedbetween the force receiving portion and the fixed portion;

a first deformable portion that connects the corresponding forcereceiving portion and the tilting portion; and

a second deformable portion that connects the corresponding fixedportion and the tilting portion,

the first deformable portion extends in a direction intersecting withthe longitudinal direction on one side of the tilting portion,

the second deformable portion extends in a direction intersecting withthe longitudinal direction on the other side of the tilting portion,

the connecting portion between the first deformable portion and thetilting portion, and the connecting portion between the seconddeformable portion and the tilting portion differ in position in thelongitudinal direction of the tilting portion,

the four displacement bodies are connected one by one to the respectivetilting portions, and are at a distance from the respective fixedportions, the four displacement bodies each including a displacementportion that is displaced by a tilting movement of the tilting portion,and

the detection circuit includes at least four capacitive elementsdisposed at least one each at the respective displacement portions, anddetects at least one of an applied force and an applied moment inaccordance with changes in capacitance values of the at least fourcapacitive elements.

With such a configuration, the displacement caused in the tiltingportion can be easily amplified by the action of the displacementportion that is displaced by the tilting movement of the tiltingportion. Further, with the capacitive elements, it is possible to detectat least an applied force or moment, in accordance with the differencesbetween the changes in the capacitance value of these capacitiveelements. That is, according to the present invention described above,it is possible to provide a force sensor that is inexpensive but highlysensitive, and is hardly affected by temperature changes and in-phasenoise in the use environment.

Each of the four displacement body may include a beam that extends in adirection intersecting with the longitudinal direction of thecorresponding tilting portion. In this case, it is possible toeffectively amplify the tilting movement caused in the tilting portion.

Each of the displacement portions of the four displacement bodies mayinclude a first displacement portion and a second displacement portiondefined at different positions from each other on the correspondingbeam,

the capacitive elements may include a total of eight capacitiveelements, the eight capacitive elements being four first capacitiveelements disposed at the first displacement portions of the respectivedisplacement bodies, and four second capacitive elements disposed at thesecond displacement portions of the respective displacement bodies, and

the detection circuit may detect at least an applied force or moment, inaccordance with changes in respective capacitance values of the eightcapacitive elements.

Alternatively, two of the four displacement bodies each include a firstdisplacement portion and a second displacement portion defined atdifferent positions from each other on the corresponding beam,

the remaining two of the four displacement bodies each include a singledisplacement portion on the corresponding beam,

the capacitive elements include a total of six capacitive elements, thesix capacitive elements being four capacitive elements disposed one byone at the respective first displacement portions and the respectivesecond displacement portions, and two capacitive elements disposed oneby one at the respective single displacement portions, and

the detection circuit may detect at least an applied force or moment, inaccordance with changes in respective capacitance values of the sixcapacitive elements.

In these cases, with the capacitive elements, it is possible to detectat least an applied force or moment with high precision, in accordancewith the differences between the changes in the capacitance value ofthese capacitive elements.

Further, the two displacement bodies including the first displacementportions and the second displacement portions may be disposed adjacentto each other via one of the fixed portions, the two displacement bodieseach including a first connecting body that connects the tilting portionof the deformable body and the beam, the first displacement portion andthe second displacement portion being disposed on both sides of thefirst connecting body, and

the two displacement bodies including the single displacement portionsmay be disposed adjacent to each other via the other one of the fixedportions, the two displacement bodies each including a second connectingbody that connects the tilting portion of the deformable body and thebeam, each displacement portion being disposed at a position ahead ofthe corresponding second connecting body or at a position behind thecorresponding second connecting body in the closed-loop path.

In these cases, with the capacitive elements, it is also possible todetect at least an applied force or moment with high precision, inaccordance with the differences between the changes in the capacitancevalue of these capacitive elements.

Of the four displacement bodies, each of the displacement bodiesincluding the first displacement portions and the second displacementportions may include a first connecting body that connects thecorresponding tilting portion and the beam, and the first displacementportion and the second displacement portion may be disposedsymmetrically with respect to the connecting portion between the firstconnecting body and the beam.

In this case, if the displacement of the tilting portion in thelongitudinal direction can be ignored, the displacement caused in thefirst displacement portion and the displacement caused in the seconddisplacement portion are of the same magnitude but have different signsfrom each other. Thus, at least an applied force or moment can bedetected through a simple calculation.

Alternatively, in each of the displacement bodies including the firstdisplacement portions and the second displacement portions among thefour displacement bodies, a displacement caused in the tilting portionand a displacement caused in one of the first displacement portion andthe second displacement portion when a force in a particular directionacts on the force receiving portion may be in the opposite directionsfrom each other and be of the same size, to prevent the one of thedisplacement portions from being displaced.

Alternatively, each of the four displacement bodies may include a singledisplacement portion on the corresponding beam,

the capacitive elements may include four capacitive elements disposedone by one at the respective displacement portions, and

each displacement body may include a connecting body that connects thetilting portion of the deformable body and the beam, and, in thecircumferential direction of the deformable body, each displacementportion may be disposed at a position ahead of the correspondingconnecting body or at a position behind the corresponding connectingbody.

Alternatively, each of the four displacement bodies may include a singledisplacement portion on the corresponding beam,

the capacitive elements may include four capacitive elements disposedone by one at the respective displacement portions,

each displacement body may include a connecting body that connects thetilting portion of the deformable body and the beam, and

each displacement portion may be disposed at a position closer to theadjacent force receiving portion than to the corresponding connectingbody.

In these cases, when the tilting portion is displaced in thelongitudinal direction, at least the applied force or moment can bedetected through a simple calculation.

The longitudinal direction of each of the tilting portions of the fourdeformable bodies may extend in a direction intersecting with the X-axisand the Y-axis in an X-Y-Z three-dimensional coordinate system,

each of the beams of the four displacement bodies may extend parallel tothe X-Y plane, and

the detection circuit may detect at least one of applied forces in therespective axis directions and applied moments around the respectiveaxes, in accordance with changes in the respective capacitance values ofthe at least four capacitive elements.

In this case, the electrode forming the capacitive element can bedisposed parallel to the X-Y plane, and thus, a force sensor can beformed with a simple structure.

Also, the force sensor may further include:

a force receiving body that is connected to the two force receivingportions of the deformable body, and receives an applied force and anapplied moment; and

a fixed body that is disposed to face each displacement body, and isconnected to the two fixed portions of the deformable body,

wherein each of the capacitive elements may include a displacementelectrode disposed on the corresponding beam, and a fixed electrodedisposed on the fixed body to face the displacement electrode.

In this case, it is possible to transmit applied forces and moments tothe deformable body without fail.

The closed-loop deformable body may have a rectangular or ring-likeshape. In this case, the deformable body has a symmetrical structure,and accordingly, the calculation for detecting applied forces andmoments is easy.

The closed-loop deformable body may be positioned on the X-Y plane tosurround the origin of an X-Y-Z three-dimensional coordinate system,

the two force receiving portions may be positioned symmetrically withrespect to the origin on the X-axis, and

the two fixed portions may be positioned symmetrically with respect tothe origin on the Y-axis.

In this case, the respective capacitive elements are symmetricallyarranged, and accordingly, the calculation for detecting applied forcesand moments is even easier.

A third mode of a force sensor according to the present inventionincludes:

a deformable body that is a closed-loop deformable body, the deformablebody including: four force receiving portions; four fixed portionsarranged together with the four force receiving portions alternatelyalong a closed-loop path; and eight deformable portions that connect theforce receiving portions and the fixed portions adjacent to one anotheralong the closed-loop path, and are elastically deformed by a force anda moment acting on the force receiving portions;

eight displacement bodies that are connected to the respectivedeformable portions, and are displaced by elastic deformation caused inthe deformable portions; and

a detection circuit that detects at least one of an applied force and anapplied moment, in accordance with displacements caused in the eightdisplacement bodies,

wherein the eight deformable portions each include:

a tilting portion that has a longitudinal direction and is disposedbetween the force receiving portion and the fixed portion;

a first deformable portion that connects the corresponding forcereceiving portion and the tilting portion; and

a second deformable portion that connects the corresponding fixedportion and the tilting portion,

the first deformable portion extends in a direction intersecting withthe longitudinal direction on one side of the tilting portion,

the second deformable portion extends in a direction intersecting withthe longitudinal direction on the other side of the tilting portion,

the connecting portion between the first deformable portion and thetilting portion, and the connecting portion between the seconddeformable portion and the tilting portion differ in position in thelongitudinal direction of the tilting portion,

the eight displacement bodies are connected one by one to the respectivetilting portions, and are at a distance from the respective fixedportions, the eight displacement bodies each including a displacementportion that is displaced by a tilting movement of the tilting portion,and

the detection circuit includes at least eight capacitive elementsdisposed at least one each at the respective displacement portions, anddetects at least one of an applied force and an applied moment inaccordance with changes in capacitance values of the at least eightcapacitive elements.

With such a configuration, the displacement caused in the tiltingportion can be easily amplified by the action of the displacementportion that is displaced by the tilting movement of the tiltingportion. Further, with the capacitive elements, it is possible to detectapplied forces, in accordance with the differences between the changesin the capacitance value of these capacitive elements. That is,according to the present invention, it is possible to provide a forcesensor that is inexpensive but highly sensitive, and is hardly affectedby temperature changes and in-phase noise in the use environment.

Each of the eight displacement body may include a beam that extends in adirection intersecting with the longitudinal direction of thecorresponding tilting portion. In this case, it is possible toeffectively amplify the tilting movement caused in the tilting portion.

Each of the displacement portions of the eight displacement bodies mayinclude a first displacement portion and a second displacement portiondefined at different positions from each other on the correspondingbeam,

the capacitive elements may include a total of 16 capacitive elements,the 16 capacitive elements being eight first capacitive elementsdisposed at the first displacement portions of the respectivedisplacement bodies, and eight second capacitive elements disposed atthe second displacement portions of the respective displacement bodies,and

the detection circuit may detect at least an applied force or moment, inaccordance with changes in respective capacitance values of the 16capacitive elements.

In this case, with the capacitive elements, it is possible to detectapplied forces with high precision, in accordance with the differencesbetween the changes in the capacitance value of these capacitiveelements.

Each of the eight displacement bodies may include a connecting body thatconnects the corresponding tilting portion and the beam, and

the first displacement portion and the second displacement portion ofeach displacement body may be disposed symmetrically with respect to theconnecting portion between the connecting body and the beam.

In this case, if the tilting portion is not displaced in itslongitudinal direction, the displacement caused in the firstdisplacement portion and the displacement caused in the seconddisplacement portion are of the same magnitude but have different signsfrom each other. Thus, the applied force can be detected through asimple calculation.

In each of the eight displacement bodies, the displacement caused in thetilting portion and the displacement caused in one of the firstdisplacement portion and the second displacement portion when a force ina particular direction acts on the force receiving portion may be inopposite directions from each other and be of the same size, to preventthe one of the displacement portions from being displaced.

In this case, the first displacement portion or the second displacementportion is disposed in such a position that the first displacementportion or the second displacement portion is not displaced when thetilting portion is displaced in its longitudinal direction. Thus, theapplied force can be detected through a simple calculation.

Each of the eight displacement bodies may include a single displacementportion on the corresponding beam,

the capacitive elements may include eight capacitive elements disposedone by one at the respective displacement portions,

each of the displacement bodies may include a second connecting bodythat connects the tilting portion of the deformable body and the beam,

the four displacement portions disposed adjacent to two fixed portionsnot adjacent to each other among the four fixed portions may be locatedon the side of the fixed portions relative to the corresponding secondconnecting body, and

the four displacement portions disposed adjacent to the remaining two ofthe four fixed portions may be located on the opposite side of thecorresponding second connecting body from the fixed portions.

In this case, the first displacement portion or the second displacementportion is also disposed in such a position that the first displacementportion or the second displacement portion is not displaced when thetilting portion is displaced in its longitudinal direction. Thus, theapplied force can be detected through a simple calculation.

The longitudinal direction of each of the tilting portions of the eightdeformable portions may extend in a direction intersecting with theX-axis and the Y-axis in an X-Y-Z three-dimensional coordinate system,

each of the first deformable portions and the second deformable portionsof the eight deformable portions, and each of the beams of the eightdisplacement bodies may extend parallel to the X-axis, and

the detection circuit may detect at least one of applied forces inrespective axis directions or applied moments around respective axes, inaccordance with changes in the respective capacitance values of the atleast eight capacitive elements,

In this case, the electrodes forming the capacitive elements can bedisposed parallel to the X-Y plane, and thus, a force sensor can beformed with a simple structure.

The force sensor may further include:

a force receiving body that is connected to the four force receivingportions of the deformable body, and receives an applied force and anapplied moment; and

a fixed body that is disposed to face the beam of each displacementbody, and is connected to the four fixed portions of the deformablebody,

wherein each of the capacitive elements may include a displacementelectrode disposed on the corresponding beam, and a fixed electrodedisposed on the fixed body to face the displacement electrode.

In this case, it is possible to transmit the applied force to thedeformable body without fail.

The closed-loop deformable body may have a rectangular or ring-likeshape. In this case, the deformable body has a symmetrical structure,and accordingly, the calculation for detecting the applied force iseasy.

The closed-loop deformable body may be positioned on the X-Y plane tosurround the origin of an X-Y-Z three-dimensional coordinate system,

two of the four force receiving portions may be disposed symmetricallywith respect to the origin on the X-axis,

the remaining two of the four force receiving portions may be disposedsymmetrically with respect to the origin on the Y-axis,

when a V-axis and a W-axis that pass through the origin and are at 45degrees to the X-axis and the −Y axis are defined on the X-Y plane,

two of the four fixed portions may be disposed symmetrically withrespect to the origin on the V-axis, and

the remaining two of the four fixed portions may be disposedsymmetrically with respect to the origin on the W-axis.

In this case, the deformable body has high symmetry, and accordingly,the calculation for detecting the applied force is easier.

The beam having only the single displacement portion may be designed asa cantilever beam supported by the second connecting body. In this case,the structure of the force sensor can be simplified.

The closed-loop deformable body may be positioned on the X-Y plane tosurround the origin of the X-Y-Z three-dimensional coordinate system,and the force receiving body may be disposed so that at least part ofthe force receiving body overlaps with the deformable body when viewedfrom the Z-axis direction.

In this case, the external size of the deformable body and the externalsize of the sensor are substantially the same when viewed from theZ-axis direction, and thus, the force sensor can be made smaller insize.

Alternatively, the closed-loop deformable body may be positioned on theX-Y plane to surround the origin of the X-Y-Z three-dimensionalcoordinate system, and

the force receiving body may be disposed on the X-Y plane to surroundthe outer circumference of the deformable body.

In this case, the deformable body and the force receiving body aredisposed in the same plane, and thus, the size of the force sensor inthe Z-axis direction can be made smaller (thinner).

In the above force sensor,

the deformable body may be disposed on the X-Y plane in an X-Y-Zthree-dimensional coordinate system,

the longitudinal direction of the tilting portion may be a directionparallel to the Z-axis,

the first deformable portion may connect the force receiving portion andthe end portion of the tilting portion on the negative Z-axis side, and

the second deformable portion may connect the fixed portion and the endportion of the tilting portion on the positive Z-axis side.

Alternatively, the deformable body may be disposed on the X-Y plane inan X-Y-Z three-dimensional coordinate system,

the longitudinal direction of the tilting portion may be a directionparallel to the Z-axis,

the first deformable portion may connect the force receiving portion andthe end portion of the tilting portion on the positive Z-axis side, and

the second deformable portion may connect the fixed portion and the endportion of the tilting portion on the negative Z-axis side.

In these cases, the tilting portion can be effectively tilted by theforce acting on the force receiving portion.

The displacement body may be attached to the end portion of the tiltingportion of the deformable body on the negative Z-axis side.

Alternatively, the displacement body may be attached to a middle portionbetween the two end portions of the tilting portion in the longitudinaldirection, the middle portion being of the tilting portion of thedeformable body.

In either case, the tilting movement of the tilting portion can betransmitted to the beam without fail.

Alternatively, the deformable body may be disposed on the X-Y plane inan X-Y-Z three-dimensional coordinate system,

the longitudinal direction of the tilting portion may be a directionintersecting with the Z-axis,

the first deformable portion may connect the force receiving portion andone end portion of the tilting portion, and

the second deformable portion may connect the fixed portion and theother end portion of the tilting portion.

With such a configuration, the tilting portion can be effectively tiltedby the force acting on the force receiving portion.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a forcesensor that is inexpensive but highly sensitive, and is hardly affectedby temperature changes and in-phase noise in the use environment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic front view of the basic structure of a forcesensor according to an embodiment of the present invention.

FIG. 2 is a schematic top view of the basic structure shown in FIG. 1.

FIG. 3 is a schematic front view of the basic structure in a deformedstate when a force +Fx in the positive X-axis direction acts on a forcereceiving portion.

FIG. 4 is a schematic front view of the basic structure in a deformedstate when a force −Fx in the negative X-axis direction acts on theforce receiving portion.

FIG. 5 is a schematic front view of the basic structure in a deformedstate when a force −Fz in the negative Z-axis direction acts on theforce receiving portion.

FIG. 6 is a schematic front view of the basic structure in a deformedstate when a force +Fz in the positive Z-axis direction acts on theforce receiving portion.

FIG. 7 is a schematic front view of an example of a force sensor thatadopts the basic structure shown in FIG. 1.

FIG. 8 is a schematic top view of the basic structure of a force sensoraccording to a second embodiment of the present invention.

FIG. 9 is a schematic front view of the basic structure as viewed fromthe positive Y-axis side in FIG. 8.

FIG. 10 is a schematic side view of the basic structure as viewed fromthe positive X-axis side in FIG. 8.

FIG. 11 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 8 when aforce +Fx in the positive X-axis direction acts on the force receivingportions.

FIG. 12 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 8 when aforce +Fy in the positive Y-axis direction acts on the force receivingportions.

FIG. 13 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 8 when aforce +Fz in the positive Z-axis direction acts on the force receivingportions.

FIG. 14 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 8 when amoment +Mx around the positive X-axis acts on the force receivingportions.

FIG. 15 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 8 when amoment +My around the positive Y-axis acts on the force receivingportions.

FIG. 16 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 8 when amoment +Mz around the positive Z-axis acts on the force receivingportions.

FIG. 17 is a table as a list that shows the displacements caused in therespective displacement bodies of the basic structure in FIG. 8 in acase where forces in the respective axis directions and moments in therespective axis directions in the X-Y-Z three-dimensional coordinatesystem act on the force receiving portions.

FIG. 18 is a schematic top view of an example of a force sensor thatadopts the basic structure shown in FIG. 8.

FIG. 19 is a schematic front view of the force sensor shown in FIG. 18as viewed from the positive Y-axis side.

FIG. 20 is a table as a list that shows increases/decreases in thecapacitance values of the respective capacitive elements in a case whereforces in the respective axis directions and moments around therespective axes in the X-Y-Z three-dimensional coordinate system act onthe force receiving portions.

FIG. 21 is a table as a list showing the other-axis sensitivities offorces in the respective axis directions and moments around therespective axes in the force sensor shown in FIG. 18.

FIG. 22 is a schematic top view of a force sensor according to a thirdembodiment of the present invention.

FIG. 23 is a table as a list showing changes in the capacitance valuesof respective capacitive elements in a case where four components offorces and moments act on the force sensor shown in FIG. 22.

FIG. 24 is a table as a list showing the other-axis sensitivities offour components of forces and moments in the force sensor shown in FIG.22.

FIG. 25 is a schematic top view of a force sensor according to amodification of FIG. 22.

FIG. 26 is a schematic top view of a force sensor according to a fourthembodiment of the present invention.

FIG. 27 is a table as a list showing changes in the capacitance valuesof respective capacitive elements in a case where four components offorces and moments act on the force sensor shown in FIG. 26.

FIG. 28 is a schematic top view of a force sensor according to amodification of FIG. 26.

FIG. 29 is a schematic top view of the basic structure of a force sensoraccording to a fifth embodiment of the present invention.

FIG. 30 is a schematic side view of the basic structure as viewed fromthe positive Y-axis side in FIG. 29.

FIG. 31 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 29 when aforce +Fx in the positive X-axis direction acts on a force receivingbody.

FIG. 32 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 29 when aforce +Fz in the positive Z-axis direction acts on the force receivingbody.

FIG. 33 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 29 when amoment +Mx around the positive X-axis acts on the force receiving body.

FIG. 34 is a diagram for explaining displacements caused in therespective displacement bodies of the basic structure in FIG. 29 when amoment +Mx around the positive Z-axis acts on the force receiving body.

FIG. 35 is a table as a list showing the directions of the tiltingmovements of the respective tilting portions and the displacementscaused in the respective displacement portions of the basic structure inFIG. 29 in a case where forces in the respective axis directions andmoments in the respective axis directions in the X-Y-Z three-dimensionalcoordinate system act on force receiving portions.

FIG. 36 is a schematic top view of a force sensor according to the fifthembodiment of the present invention using the basic structure shown inFIG. 29.

FIG. 37 is a schematic side view of the force sensor as viewed from thepositive X-axis side in FIG. 36.

FIG. 38 is a table as a list showing changes in the capacitance valuesof respective capacitive elements in a case where six components offorces and moments act on the force sensor shown in FIG. 36.

FIG. 39 is a table as a list showing the other-axis sensitivities offour components of forces and moments in the force sensor shown in FIG.36.

FIG. 40 is a schematic top view of a force sensor according to a sixthembodiment of the present invention.

FIG. 41 is a schematic front view of the force sensor shown in FIG. 40as viewed from the positive Y-axis side.

FIG. 42 is a table as a list showing changes in the capacitance valuesof respective capacitive elements in a case where six components offorces and moments act on the force sensor shown in FIG. 40.

FIG. 43 is a table as a list showing the other-axis sensitivities of thesix components of forces and moments in the force sensor shown in FIG.40.

FIG. 44 is a schematic top view of a force sensor according to a seventhembodiment of the present invention.

FIG. 45 is a table as a list showing the directions of the tiltingmovements of the respective tilting portions and the displacementscaused in the respective displacement portions of the force sensor shownin FIG. 44 in a case where forces in the respective axis directions andmoments in the respective axis directions in the X-Y-Z three-dimensionalcoordinate system act on force receiving portions.

FIG. 46 is a schematic top view of a force sensor according to amodification of FIG. 44.

FIG. 47 is a schematic top view of the basic structure of a force sensoraccording to an eighth embodiment of the present invention.

FIG. 48 is a schematic top view of the basic structure shown in FIG. 47.

FIG. 49 is a schematic front view of the basic structure in a deformedstate when a force −Fx in the negative X-axis direction acts on a forcereceiving portion.

FIG. 50 is a table as a list showing the changes caused in thecapacitance values of the capacitive elements when forces in therespective axis directions and moments around the respective axes act ona force sensor according to a modification of FIG. 47.

FIG. 51 is a table as a list showing the other-axis sensitivities of sixcomponents of forces and moments in the force sensor corresponding toFIG. 50.

FIG. 52 is a table as a list showing the other-axis sensitivities ofcomponents in the force sensor corresponding to FIG. 50 in a case wherethe other-axis sensitivities are calculated according to differentexpressions from those in the case of FIG. 51.

FIG. 53 is a table as a list showing the changes caused in thecapacitance values of the capacitive elements when forces in therespective axis directions and moments around the respective axes act ona force sensor according to a further modification of FIG. 47.

FIG. 54 is a table as a list showing the other-axis sensitivities of sixcomponents of forces and moments in the force sensor corresponding toFIG. 53.

FIG. 55 is a schematic cross-sectional view of an example of the basicstructure of a force sensor in which a force receiving body is disposedon the outer circumferential side of a deformable body.

FIG. 56 is a schematic side view of a modification of the force sensoraccording to the first embodiment.

FIG. 57 is a schematic side view of a further modification of FIG. 56.

FIG. 58 is a schematic side view of a further modification of FIG. 56.

FIG. 59 is a schematic top view of a force sensor according to amodification of FIG. 18.

DESCRIPTION OF EMBODIMENTS § 1. Force Sensor According to a FirstEmbodiment of the Present Invention

<1-1. Configuration of a Basic Structure>

Referring to the accompanying drawings, a force sensor according to afirst embodiment of the present invention is described.

FIG. 1 is a schematic front view of a basic structure 100 of a forcesensor according to one embodiment of the present invention. FIG. 2 is aschematic top view of the basic structure 100. This embodiment isdescribed below, with the X-Y-Z three-dimensional coordinate systembeing defined as shown in FIGS. 1 and 2,

As shown in FIGS. 1 and 2, the basic structure 100 includes: adeformable body 10 that has a force receiving portion 14 and a fixedportion 15, and causes elastic deformation with a force acting on theforce receiving portion 14; and a displacement body 20 that is connectedto the deformable body 10 and causes displacement through elasticdeformation caused in the deformable body 10. The force receivingportion 14 is a portion for receiving a force to be detected, and thefixed portion 15 is a portion that does not displace even when a forceacts on the force receiving portion 14.

As shown in FIGS. 1 and 2, the deformable body 10 includes: a tiltingportion 13 has a longitudinal direction 1 parallel to the Z-axis, and isdisposed between the force receiving portion 14 and the fixed portion15; a first deformable portion 11 connecting the force receiving portion14 and the tilting portion 13; and a second deformable portion 12connecting the fixed portion 15 and the tilting portion 13. As shown inthe drawing, the first deformable portion 11 extends in a directionintersecting with the longitudinal direction 1 on one side (the leftside in FIGS. 1 and 2) of the tilting portion 13. On the other hand, thesecond deformable portion 12 extends in the direction intersecting withthe longitudinal direction 1 on the other side (the right side in FIGS.1 and 2) of the tilting portion 13. In the example illustrated in thedrawing, the direction intersecting with the longitudinal direction 1 isthe X-axis direction.

Further, the connecting portion R1 between the first deformable portion11 and the tilting portion 13, and the connecting portion R2 between thesecond deformable portion 12 and the tilting portion 13 differ inposition in the longitudinal direction 1 of the tilting portion 13.Specifically, the connecting portion R1 is located in the vicinity ofthe end portion on the negative Z-axis side (the lower end portion inFIG. 1) of the tilting portion 13, and the connecting portion R2 islocated in the vicinity of the end portion on the positive Z-axis side(the upper end portion in FIG. 1) of the tilting portion 13.

As shown in FIGS. 1 and 2, both the force receiving portion 14 and thefixed portion 15 extend parallel to the Z-axis. The respective upper endportions of the force receiving portion 14, the tilting portion 13, andthe fixed portion 15 have the same position in the Z-axis direction. Therespective lower end portions of the force receiving portion 14 and thetilting portion 13 also have the same position in the Z-axis direction.The lower end portion of the force receiving portion 14 and the lowerend portion of the tilting portion 13 are connected by the firstdeformable portion 11 extending parallel to the X-axis, and the upperend portion of the tilting portion 13 and the upper end portion of thefixed portion 15 are connected by the second deformable portion 12extending parallel to the X-axis. Further, the lower end portion of thefixed portion 15 is connected to a support 50 disposed to face thetilting portion 13 at a predetermined distance.

As shown in FIGS. 1 and 2, the displacement body 20 has a beam 21connected to the tilting portion 13 via a connecting body 22 attached tothe lower end of the tilting portion 13. The beam 21 extends in adirection orthogonal to the longitudinal direction 1 of the tiltingportion 13, and has a symmetrical shape when viewed from the Y-axisdirection. The beam 21 is at a distance from the fixed portion 15 andthe force receiving portion 14 of the deformable body 10 so that tilting(turning) of the beam 21 is not hindered by the fixed portion 15 and theforce receiving portion 14. In the beam 21, a first displacement portionD1 and a second displacement portion D2 are defined symmetrically withrespect to the connecting portion between the beam 21 and the connectingbody 22. As will be described later, capacitive elements are disposed inthe first displacement portion D1 and the second displacement portion D2so that a force acting on the force receiving portion 14 is detected.

<1-2. Operation of the Basic Structure>

Next, operation of the above basic structure 100 is described.

FIG. 3 is a schematic front view of the basic structure 100 in adeformed state when a force +Fx in the positive X-axis direction acts onthe force receiving portion 14. FIG. 4 is a schematic front view of thebasic structure 100 in a deformed state when a force −Fx in the negativeX-axis direction acts on the force receiving portion 14. FIG. 5 is aschematic front view of the basic structure 100 in a deformed state whena force −Fz in the negative Z-axis direction acts on the force receivingportion 14. FIG. 6 is a schematic front view of the basic structure 100in a deformed state when a force +Fz in the positive Z-axis directionacts on the force receiving portion 14.

(1-2-1, Where a Force +Fx is Applied)

When a force +Tx in the positive X-axis direction acts on the forcereceiving portion 14, a force in the positive X-axis direction (therightward direction in FIG. 3) acts on the connecting portion R1 in thevicinity of the lower end of the tilting portion 13, and a force in thenegative X-axis direction (the leftward direction in FIG. 3) acts as areaction of the applied force +Fx on the connecting portion R2 in thevicinity of the upper end of the tilting portion 13. Because of theactions of these forces, the tilting portion 13 tilts counterclockwiseas shown in FIG. 3. Both the first deformable portion 11 and the seconddeformable portion 12 are of course compressively deformed by the actionof the applied force +Fx, and accordingly, the entire tilting portion 13is slightly displaced in the positive X-axis direction.

Due to such tilting movement of the tilting portion 13, the beam 21connected to the lower end of the tilting portion 13 also tiltscounterclockwise as shown in FIG. 3. As a result, the first displacementportion D1 of the beam 21 is displaced in the direction (the downwarddirection in FIG. 3) in which the distance to the support 50 decreases,and the second displacement portion D2 is displaced in the direction(the upward direction in FIG. 3) in which the distance to the support 50increases.

(1-2-2. Where a Force −Fx is Applied)

When a force −Fx in the negative X-axis direction acts on the forcereceiving portion 14, on the other hand, a force in the negative X-axisdirection (the leftward direction in FIG. 4) acts on the connectingportion R1 in the vicinity of the lower end of the tilting portion 13,and a force in the positive X-axis direction (the rightward direction inFIG. 4) acts as a reaction of the applied force −Fx on the connectingportion R2 in the vicinity of the upper end of the tilting portion 13.Because of the actions of these forces, the tilting portion 13 tiltsclockwise as shown in FIG. 4. Both the first deformable portion 11 andthe second deformable portion 12 are of course tensile-deformed by theaction of the applied force −Fx, and accordingly, the entire tiltingportion 13 is slightly displaced in the negative X-axis direction.

Due to such tilting movement of the tilting portion 13, the beam 21connected to the lower end of the tilting portion 13 also tiltsclockwise as shown in FIG. 4. As a result, the first displacementportion D1 of the beam 21 is displaced in the direction (the upwarddirection in FIG. 4) in which the distance to the support 50 increases,and the second displacement portion D2 is displaced in the direction(the downward direction in FIG. 4) in which the distance to the support50 decreases.

(1-2-3. Where a Force −Fz is Applied)

When a force −Fz in the negative Z-axis direction acts on the forcereceiving portion 14, a force in the negative Z-axis direction (thedownward direction in FIG. 5) acts on the connecting portion R1 at thelower left end of the tilting portion 13, and a force in the positiveZ-axis direction (the upward direction in FIG. 5) acts as a reaction ofthe applied force −Fz on the connecting portion R2 at the upper rightend of the tilting portion 13. Because of the actions of these forces,the tilting portion 13 tilts counterclockwise as shown in FIG. 5.Furthermore, because of the action of the applied force −Fz, the tiltingportion 13 is pulled downward in the negative Z-axis direction via thefirst deformable portion 11, and accordingly, the entire tilting portion13 is slightly displaced in the negative Z-axis direction.

Due to the tilting movement of the tilting portion 13, the beam 21connected to the lower end of the tilting portion 13 also tiltscounterclockwise as shown in FIG. 5. As a result, the first displacementportion D1 of the beam 21 is displaced in the direction (the downwarddirection in FIG. 5) in which the distance to the support 50 decreases,and the second displacement portion D2 is displaced in the direction(the upward direction in FIG. 5) in which the distance to the support 50increases.

Depending on the length of the beam 21, the displacement of the seconddisplacement portion D2 in the positive Z-axis direction might besmaller than the displacement of the entire beam 21 in the negativeZ-axis direction, and the distance between the second displacementportion D2 and the support 50 might decrease. However, the beam 21 has asufficient length in this example, and such a situation does not occur.

(1-2-4. Where a Force +Fz is Applied)

When a force +Fz in the positive Z-axis direction acts on the forcereceiving portion 14, a force in the positive Z-axis direction (theupward direction in FIG. 6) acts on the connecting portion R1 at thelower left end of the tilting portion 13, and a force in the negativeZ-axis direction (the downward direction in FIG. 6) acts as a reactionof the applied force +Fz on the connecting portion R2 at the upper rightend of the tilting portion 13. Because of the actions of these forces,the tilting portion 13 tilts clockwise as shown in FIG. 6. Because ofthe action of the applied force +Fz, the tilting portion 13 is of coursepulled upward in the positive Z-axis direction via the first deformableportion 11, and accordingly, the entire tilting portion 13 is slightlydisplaced in the positive Z-axis direction.

Due to such tilting movement of the tilting portion 13, the beam 21connected to the lower end of the tilting portion 13 also tiltsclockwise as shown in FIG. 6. As a result, the first displacementportion D1 of the beam 21 is displaced in the direction (the upwarddirection in FIG. 6) in which the distance to the support 50 increases,and the second displacement portion D2 is displaced in the direction(the downward direction in FIG. 6) in which the distance to the support50 decreases.

Depending on the length of the beam 21, the displacement of the seconddisplacement portion D2 in the negative Z-axis direction might besmaller than the displacement of the entire beam 21 in the positiveZ-axis direction, and the distance between the second displacementportion D2 and the support 50 might increase. However, the beam 21 has asufficient length in this example, and such a situation does not occur.

In any of the above cases, the displacement caused in the firstdisplacement portion D1 and the second displacement portion D2 is largerthan the displacement caused in the lower end of the tilting portion 13.That is, because of the existence of the beam 21, the displacementcaused in the lower end portion of the tilting portion 13 is amplifiedand taken out as the displacement in the Z-axis direction at each of thedisplacement portions D1 and D2 of the beam 21.

<1-3. Structure of a Force Sensor>

Next, the structure of a force sensor 100 c including the basicstructure 100 described above in 1-1 and 1-2 is described.

FIG. 7 is a schematic front view of an example of the force sensor 100 cthat adopts the basic structure 100 shown in FIG. 1.

As shown in FIG. 7, the force sensor 100 c includes the above describedbasic structure 100 and a detection circuit 40 that detects an appliedforce in accordance with displacements caused in the first displacementportion D1 and the second displacement portion D2 of the beam 21 of thebasic structure 100. As shown in FIG. 7, the detection circuit 40 ofthis embodiment includes: a first capacitive element C1 disposed at thefirst displacement portion D1; a second capacitive element C2 disposedat the second displacement portion D2; and a measuring unit 41 that isconnected to the capacitive elements C1 and C2, and measures the appliedforce in accordance with changes in the capacitance values of thecapacitive elements C1 and C2.

As shown in FIG. 7, the first capacitive element C1 includes: a firstdisplacement electrode Em1 disposed on the first displacement portion D1of the beam 21 via an insulator; and a first fixed electrode Ef1disposed on the support 50 via an insulator in such a manner as to facethe first displacement electrode Em1. Likewise, the second capacitiveelement C2 includes: a second displacement electrode Em2 disposed on thesecond displacement portion D2 of the beam 21 via an insulator; and asecond fixed electrode Ef2 disposed on the support 50 via an insulatorin such a manner as to face the second displacement electrode Em2.Although not clearly shown in FIG. 7, these capacitive elements C1 andC2 are connected to the measuring unit 41 by a predetermined circuit,and the capacitance values of the capacitive elements C1 and C2 aresupplied to the measuring unit 41.

In the drawing, the first displacement electrode Em1, the seconddisplacement electrode Em2, the first fixed electrode Ef1, and thesecond fixed electrode Ef2 are formed with individual electrodes. Inother embodiments, however, the first displacement electrode Em1 and thesecond displacement electrode Em2, or the first fixed electrode Ef1 andthe second fixed electrode Ef2 may be formed with a common electrode.This also applies to the other embodiments described in § 2 and later.

<1-4. Operation of the Force Sensor>

Next, operation of the force sensor 100 c described in 1-3 is described.

(1-4-1. Where a Force Fx is Applied)

When a force +Tx in the positive X-axis direction acts on the forcereceiving portion 14 of the force sensor 100 c, the distance between thefirst displacement electrode Em1 and the first fixed electrode ET1decreases in the first capacitive element C1, and the distance betweenthe second displacement electrode Em2 and the second fixed electrode Ef2increases in the second capacitive element C2, as can be seen from thebehavior of the beam 21 described in 1-2 with reference to FIG. 3. Thatis, the capacitance value of the first capacitive element C1 increases,and the capacitance value of the second capacitive element C2 decreases.

In this embodiment, the first capacitive element C1 and the secondcapacitive element C2 are arranged at equal distances from the center oftilting movement of the beam 21, as can be seen from the layout of thefirst displacement portion D1 and the second displacement portion D2.Accordingly, the magnitude (|ΔC1|) of the change in the capacitancevalue of the first capacitive element C1 is equal to the magnitude(|ΔC2|) of the change in the capacitance value of the second capacitiveelement C2. Because of this, where |ΔC1|=|ΔC2|=ΔC, the respectivecapacitance values C1 a and C2 a of the first capacitive element C1 andthe second capacitive element C2 at a time when a force +Fx is appliedare expressed by [Expression 1] shown below.

In [Expression 1], C1 and C2 represent the capacitance values of thefirst and second capacitive elements C1 and C2, respectively, at a timewhen no force is applied. This also applies to each of the expressionsthat will be shown later.C1a=C1+ΔCC2a=C2−ΔC  [Expression 1]

In accordance with such changes in the capacitance values, the measuringunit 41 measures the applied force +Fx by using the following[Expression 2]. In [Expression 2], the force and the capacitance valuesare connected with “=”. However, these are different physicalquantities, and therefore, the force +Fx is measured after predeterminedconversion is performed. This notation is used not only in [Expression2] but also in the expressions that will be shown later.+Fx=C1−C2  [Expression 2]

When a force −Fx in the negative X-axis direction acts on the forcereceiving portion 14 of the force sensor 100 c, on the other hand, thedistance between the first displacement electrode Em1 and the firstfixed electrode Ef1 increases in the first capacitive element C1, andthe distance between the second displacement electrode Em2 and thesecond fixed electrode Ef2 decreases in the second capacitive elementC2, as can be seen from the behavior of the beam 21 described in 1-2with reference to FIG. 4. That is, the capacitance value of the firstcapacitive element C1 decreases, and the capacitance value of the secondcapacitive element C2 increases. In short, all the signs should be theopposite of those in the above described case where the force +Fx isapplied.

Therefore, the measuring unit 41 measures the applied force −Fxaccording to the following [Expression 3],−Fx=C2−C1  [Expression 3]

In other words, [Expression 2] and [Expression 3] are the samearithmetic expressions, and, in either case, the applied force Fx ismeasured according to the expression, Fx=C1−C2.

(1-4-2. Where a Force Fz is Applied)

When a force −Fz in the negative Z-axis direction acts on the forcereceiving portion 14 of the force sensor 100 c, on the other hand, thedistance between the first displacement electrode Em1 and the firstfixed electrode Ef1 decreases in the first capacitive element C1, andthe distance between the second displacement electrode Em2 and thesecond fixed electrode Ef2 increases in the second capacitive elementC2, as can be seen from the behavior of the beam 21 described in 1-2with reference to FIG. 5. That is, the capacitance value of the firstcapacitive element C1 increases, and the capacitance value of the secondcapacitive element C2 decreases.

More specifically, the displacement caused in the first displacementportion D1 when the force −Fz is applied is the sum of the overalldisplacement of the above described tilting portion 13 in the negativeZ-axis direction and the displacement in the negative Z-axis directiondue to the tilting movement of the beam 21, and the displacement causedin the second displacement portion D2 is the sum of the overalldisplacement of the tilting portion 13 in the negative Z-axis directionand the displacement in the positive Z-axis direction due to the tiltingmovement of the beam 21. In other words, if the changes in thecapacitance values of the respective capacitive elements C1 and C2 aremore accurately described, in the first capacitive element C1, theoverall displacement of the tilting portion 13 in the negative Z-axisdirection is added to the displacement due to the tilting movement ofthe beam 21, and therefore, the distance between the first displacementelectrode Em1 and the first fixed electrode Ef1 greatly degreases. Inthe second capacitive element C2, on the other hand, the displacementdue to the tilting movement of the beam 21 is offset by the overalldisplacement of the tilting portion 13 in the negative Z-axis direction,and therefore, the distance between the second displacement electrodeEm2 and the second fixed electrode Ef2 slightly increases.

However, for simplicity, the length of the beam 21 in the Z-axisdirection is sufficiently greater than the length (height) of thetilting portion 13 in the Z-axis direction as described above, so thatthe magnitude (|ΔC1|) of the change in the capacitance value of thefirst capacitive element C1 and the magnitude (|ΔC2|) of the change inthe capacitance value of the second capacitive element C2 can beconsidered to be substantially equal. Accordingly, where |ΔC1|=|ΔC2|=ΔC,the respective capacitance values C1 b and C2 b of the first capacitiveelement C1 and the second capacitive element C2 at a time when the force−Fz is applied are expressed by the following [Expression 4].C1b=C1−ΔCC2b=C2+ΔC  [Expression 4]

In accordance with such changes in the capacitance values, the measuringunit 41 measures the applied force −Fz by using the following[Expression 5].−Fz=C1−C2  [Expression 5]

When a force +Fz in the positive Z-axis direction acts on the forcereceiving portion 14 of the force sensor 100 c, on the other hand, thedistance between the first displacement electrode Em1 and the firstfixed electrode Ef1 increases in the first capacitive element C1, andthe distance between the second displacement electrode Em2 and thesecond fixed electrode Ef2 decreases in the second capacitive elementC2, as can be seen from the behavior of the beam 21 described in 1-2with reference to FIG. 6. That is, the capacitance value of the firstcapacitive element C1 decreases, and the capacitance value of the secondcapacitive element C2 increases. In this case, the magnitude (|ΔC1|) ofthe change in the capacitance value of the first capacitive element C1and the magnitude (|ΔC2|) of the change in the capacitance value of thesecond capacitive element C2 can be considered to be substantiallyequal, as in the case where the force −Fz is applied.

Therefore, in accordance with the above changes in the capacitancevalues, the measuring unit 41 measures the applied force +Fz by usingthe following [Expression 6].+Fz=C2−C1  [Expression 6]

In other words, [Expression 5] and [Expression 6] are the samearithmetic expressions, and, in either case, the applied force Fz ismeasured according to the expression, Fz=C2−C1.

Comparison among the above [Expression 2], [Expression 3], [Expression5], and [Expression 6] shows that the right side of [Expression 2] isidentical to the right side of [Expression 5], and the right side of[Expression 3] is identical to the right side of [Expression 6].Therefore, as for [Expression 2] and [Expression 5], the measuring unit41 cannot determine whether the applied force is +Fx or −Fz. Likewise,as for [Expression 3] and [Expression 6], the measuring unit 41 cannotdetermine whether the applied force is −Fx or +Fz. However, in anenvironment where forces in only one direction, the X-axis direction orthe Z-axis direction, are applied, the measuring unit 41 can measure thedirection (the sign) and the magnitude of the applied force through adifference calculation.

According to this embodiment described above, the displacement portionsD1 and D2 are displaced by the tilting motion of the tilting portion 13,so that the tilting generated in the tilting portion 13 can beeffectively amplified. Thus, the inexpensive but highly sensitive forcesensor 1100 c can be provided. Further, the measuring unit 41 calculatesthe capacitance value of the first capacitive element C1 disposed at thefirst displacement portion D1 and the capacitance value of the secondcapacitive element C2 disposed at the second displacement portion D2.Thus, the force sensor 100 c that is hardly affected by temperaturechanges in the usage environment and in-phase noise can be provided.

Further, the first displacement portion D1 and the second displacementportion D2 of the displacement body 20 are formed on the beam 21symmetrically with respect to the connecting portion between theconnecting body 22 and the beam 21. Accordingly, the displacement causedin the first displacement portion D1 and the displacement caused in thesecond displacement portion D2 are of the same magnitude but havedifferent signs from each other. Thus, the applied force can be detectedthrough a simple calculation.

§ 2. Force Sensor According to a Second Embodiment of the PresentInvention

<2-1. Configuration of a Basic Structure>

Next, a force sensor according to a second embodiment of the presentinvention is described.

FIG. 8 is a schematic top view of a basic structure 200 of a forcesensor 200 c according to the second embodiment of the presentinvention. FIG. 9 is a schematic front view of the basic structure 200viewed from the positive Y-axis side in FIG. 8. FIG. 10 is a schematicside view of the basic structure 200 viewed from the positive X-axisside in FIG. 8. This embodiment is described below, with the X-Y-Zthree-dimensional coordinate system being defined as shown in FIGS. 8through 10. For ease of explanation, a force receiving body 260 is notshown in FIG. 8.

As shown in FIGS. 8 through 10, the basic structure 200 includes adeformable body that is a closed-loop deformable body, and fourdisplacement bodies 220A through 220D. The deformable body includes: twoforce receiving portions 218 and 219; two fixed portions 216 and 217arranged together with the two force receiving portions 218 and 219alternately along a closed-loop path; and four deformable elements 210Athrough 210D that are disposed one by one in the four spaces formedbetween the force receiving portions 218 and 219 and the fixed portions216 and 217, which are adjacent to one another along the closed-looppath, and are elastically deformed by a force or a moment acting on theforce receiving portions 218 and 219. The displacement bodies 220Athrough 220D are connected to the deformable elements 210A through 210D,respectively, and are displaced by elastic deformation caused in thedeformable elements 210A through 210D.

In this embodiment, the force receiving portion 218 is disposed on thepositive X-axis, and the other force receiving portion 219 is disposedon the negative X-axis, symmetrically with respect to the origin O, asshown in FIG. 8. Also, the fixed portion 216 is disposed on the positiveY-axis, and the other fixed portion 217 is disposed on the negativeY-axis, symmetrically with respect to the origin O. In this embodiment,the closed-loop deformable body including the force receiving portions218 and 219 and the fixed portions 216 and 217 is formed as an annulardeformable body 210 having a circular shape with the origin O as itscenter.

As shown in FIGS. 8 through 10, the first deformable element 210Adisposed in the second quadrant of the plane when viewed from the Z-axisdirection is located like an arc between the force receiving portion 219disposed on the negative X-axis side and the fixed portion 216 disposedon the positive Y-axis side. The first deformable element 210A includesa first tilting portion 213A having the Z-axis direction (the depthdirection in FIG. 8) as its longitudinal direction, a 1-1st deformableportion 211A connecting the force receiving portion 219 and the firsttilting portion 213A, and a 1-2nd deformable portion 212A connecting thefixed portion 216 and the first tilting portion 213A. As shown in FIG.9, the 1-1st deformable portion 211A extends parallel to the X-Y plane,and is connected to the first tilting portion 213A at the end portion(the lower end) of the first tilting portion 213A on the negative Z-axisside. The 1-2nd deformable portion 212A extends parallel to the X-Yplane, and is connected to the first tilting portion 213A at the endportion (the upper end) of the first tilting portion 213A on thepositive Z-axis side.

The second deformable element 210B disposed in the first quadrant of theX-Y plane when viewed from the Z-axis direction is located like an arcbetween the force receiving portion 218 disposed on the positive X-axisside and the fixed portion 216 disposed on the positive Y-axis side. Thesecond deformable element 210B includes a second tilting portion 213Bhaving the Z-axis direction (the depth direction in FIG. 8) as itslongitudinal direction, a 2-1st deformable portion 211B connecting theforce receiving portion 218 and the second tilting portion 213B, and a2-2nd deformable portion 212B connecting the fixed portion 216 and thesecond tilting portion 213B. As shown in FIG. 9, the 2-1st deformableportion 211B extends parallel to the X-Y plane, and is connected to thesecond tilting portion 213B at the end portion (the lower end) of thesecond tilting portion 213B on the negative Z-axis side. The 2-2nddeformable portion 212B extends parallel to the X-Y plane, and isconnected to the second tilting portion 213B at the end portion (theupper end) of the second tilting portion 213B on the positive Z-axisside.

Although not specifically shown in the drawing, the fourth deformableelement 210D and the third deformable element 210C disposed in the thirdquadrant and the fourth quadrant of the X-Y plane correspond to theabove described configurations of the second deformable element 210B andthe first deformable element 210A, respectively, when the portion of theannular deformable body 210 on the positive Y-axis side (the upper halfof the annular deformable body 210 in FIG. 8) is rotated 180 degreesaround the origin. Therefore, detailed explanation thereof is not madeherein. In FIGS. 8 through 10, “C” is attached to the reference numeralof each component of the third deformable element 210C, and “D” isattached to the reference numeral of each component of the fourthdeformable element 210D. Further, the lower end portions of therespective fixed portions 216 and 217 of the basic structure 200 areconnected to a support 250, with a predetermined distance being keptfrom first through fourth beams 221A through 221D that will be describedlater.

As shown in FIGS. 8 through 10, the above described four displacementbodies 220A through 220D are connected one by one to the lower ends (theend on the negative Z-axis side) of the respective tilting portions 213Athrough 213D of the first through fourth deformable elements 210Athrough 210D. Each of the displacement bodies 220A through 220D has adisplacement portion that is displaced by the tilting movement of thecorresponding one of the tilting portions 213A through 213D. As shown inFIGS. 8 through 10, the displacement portions are the first throughfourth beams 221A through 221D attached to the lower ends of the tiltingportions 213A through 213D via connecting bodies 222A through 222D,respectively.

These beams 221A through 221D extend in a direction orthogonal to thelongitudinal direction (the Z-axis direction) of the correspondingtilting portions 213A through 213D, and each of the beams 221A through221D has a symmetrical shape when viewed from the radial direction ofthe annular deformable body 210. Each of the beams 221A through 221D isat a distance from the fixed portions 216 and 217 and the forcereceiving portions 218 and 219 so that the tilting (turning) of thebeams 221A through 221D is not disturbed. In the first beam 221A, a1-1st displacement portion D11 and a 1-2nd displacement portion D12 aredefined symmetrically with respect to the connecting portion between thefirst beam 221A and the first connecting body 222A. Likewise, in thesecond beam 221B, a 2-1st displacement portion D21 and a 2-2nddisplacement portion D22 are defined symmetrically with respect to theconnecting portion between the second beam 221B and the secondconnecting body 222B. In the third beam 221C, a 3-1st displacementportion D31 and a 3-2nd displacement portion D32 are definedsymmetrically with respect to the connecting portion between the thirdbeam 221C and the third connecting body 222C. In the fourth beam 221D, a4-1st displacement portion D41 and a 4-2nd displacement portion D42 aredefined symmetrically with respect to the connecting portion between thefourth beam 221D and the fourth connecting body 222D. As will bedescribed later, capacitive elements are disposed in the respective1-1st through 4-2nd displacement portions D11 through D42, so thatforces and moments acting on the force receiving portions 218 and 219are detected. In short, the basic structure 200 is formed with fourbasic structures 100 as the first through fourth deformable elements210A through 210D arranged in a ring-like form, and each of the fourbasic structures 100 is the basic structure 100 described in § 1.

Further, as shown in 9 and 10, the force receiving body 260 forreceiving the force to be detected is disposed on the positive Z-axisside of the annular deformable body 210. The force receiving body 260includes: a force receiving body main body 261 having a ring-like shapethat is exactly the same shape as the annular deformable body 210 whenviewed from the Z-axis direction; and force receiving portion connectingbodies 262 and 263 provided on the portions of the force receiving bodymain body 261 facing the force receiving portions 218 and 219 of theannular deformable body 210. The force receiving portion connectingbodies 262 and 263 are connected to the corresponding force receivingportions 218 and 219, so that a force and a moment acting on the forcereceiving body main body 261 are transmitted to the respective forcereceiving portions 218 and 219.

<2-2, Operation of the Basic Structure>

Next, operation of the above basic structure 200 is described.

(2-2-1. Where a Force +Fx is Applied)

FIG. 11 is a diagram for explaining displacements caused in therespective displacement bodies 220A through 220D of the basic structure200 in FIG. 8 when a force +Fx in the positive X-axis direction acts onthe force receiving portions 218 and 219. In FIG. 8, forces acting onthe force receiving portions 218 and 219 are indicated by thick solidarrows.

The tilting movements caused in the tilting portions 213A through 213Dof the respective deformable elements 210A through 210D are indicated bythin arcuate arrows. The arrows indicate the directions of the tiltingmovements (clockwise or counterclockwise) of the respective tiltingportions 213A through 213D when viewed from the origin O. Further, theZ-axis direction displacements caused in the respective displacementportions D11 through D42 of the beams 221A through 221D of thedisplacement bodies 220A through 220D due to the tilting movements ofthe respective tilting portions 213A through 213D are indicated by dotsenclosed in circles and crosses enclosed by circles. The dots enclosedby circles indicate displacements from the back side to the front side(displacements in the positive Z-axis direction), and the crossesenclosed by circles indicate displacements from the front side to theback side (displacements in the negative Z-axis direction). It should benoted that this diagrammatic representation is also used in each of theembodiments described later. Forces acting on the force receivingportions 218 and 219 are indicated by a dot enclosed by a circle and across enclosed by a circle, depending on their orientations. Themeanings of these symbols are as described above.

When a force +Fx in the positive X-axis direction acts on the forcereceiving portions 218 and 219 via the force receiving body 260, theforce receiving portions 218 and 219 are displaced in the positiveX-axis direction, as shown in FIG. 11. Because of this, the firstdeformable element 210A is subjected to compressive force like thecompressive force shown in FIG. 3. In this case, the first tiltingportion 213A tilts counterclockwise, and therefore, the first beam 221Aalso tilts counterclockwise. As a result, the 1-1st displacement portionD11 is displaced in the negative Z-axis direction, and the 1-2nddisplacement portion D12 is displaced in the positive Z-axis direction.

The second deformable element 210B is subjected to tensile force likethe tensile force shown in FIG. 4, due to the displacement of the forcereceiving portion 218 in the positive X-axis direction. In this case,the second tilting portion 213B tilts counterclockwise, and therefore,the second beam 221B also tilts counterclockwise. As a result, the 2-1stdisplacement portion D21 is displaced in the negative Z-axis direction,and the 2-2nd displacement portion D22 is displaced in the positiveZ-axis direction.

The third deformable element 210C is subjected to tensile force like thetensile force shown in FIG. 4, due to the displacement of the forcereceiving portion 218 in the positive X-axis direction. In this case,the third tilting portion 213C tilts clockwise, and therefore, the thirdbeam 221C also tilts clockwise. As a result, the 3-1st displacementportion D31 is displaced in the positive Z-axis direction, and the 3-2nddisplacement portion D32 is displaced in the negative Z-axis direction.

Further, the fourth deformable element 210D is subjected to compressiveforce like the compressive force shown in FIG. 3, due to thedisplacement of the force receiving portion 219 in the positive X-axisdirection. In this case, the fourth tilting portion 213D tiltsclockwise, and therefore, the fourth beam 221D also tilts clockwise. Asa result, the 4-1st displacement portion D41 is displaced in thepositive Z-axis direction, and the 4-2nd displacement portion D42 isdisplaced in the negative Z-axis direction.

(2-2-2. Where a Force +Fy is Applied)

FIG. 12 is a diagram for explaining displacements caused in therespective displacement bodies 220A through 220D of the basic structure200 in FIG. 8 when a force +Fy in the positive Y-axis direction acts onthe force receiving portions 218 and 219.

When a force +Fy in the positive Y-axis direction acts on the forcereceiving portions 218 and 219 via the force receiving body 260, theforce receiving portions 218 and 219 are displaced in the positiveY-axis direction, as shown in FIG. 12. Because of this, the firstdeformable element 210A is subjected to compressive force like thecompressive force shown in FIG. 3. In this case, the first tiltingportion 213A and the first beam 221A tilt counterclockwise, as describedabove. Therefore, the 1-1st displacement portion D11 is displaced in thenegative Z-axis direction, and the 1-2nd displacement portion D12 isdisplaced in the positive Z-axis direction.

The second deformable element 210B is subjected to compressive forcelike the compressive force shown in FIG. 3, due to the displacement ofthe force receiving portion 218 in the positive Y-axis direction. Inthis case, the second tilting portion 213B and the second beam 221B tiltclockwise. Therefore, the 2-1st displacement portion D21 is displaced inthe positive Z-axis direction, and the 2-2nd displacement portion D22 isdisplaced in the negative Z-axis direction.

The third deformable element 210C is subjected to tensile force like thetensile force shown in FIG. 4, due to the displacement of the forcereceiving portion 218 in the positive Y-axis direction. In this case,the third tilting portion 213C and the third beam 221C tilt clockwise.Therefore, the 3-1st displacement portion D31 is displaced in thepositive Z-axis direction, and the 3-2nd displacement portion D32 isdisplaced in the negative Z-axis direction.

The fourth deformable element 210D is subjected to tensile force likethe tensile force shown in FIG. 4, due to the displacement of the forcereceiving portion 219 in the positive Y-axis direction. In this case,the fourth tilting portion 213D and the fourth beam 221D tiltcounterclockwise. Therefore, the 4-1st displacement portion D41 isdisplaced in the negative Z-axis direction, and the 4-2nd displacementportion D42 is displaced in the positive Z-axis direction.

(2-2-3. Where a Force +Fz is Applied)

FIG. 13 is a diagram for explaining displacements caused in therespective displacement bodies 220A through 220D of the basic structure200 in FIG. 8 when a force +Fz in the positive Z-axis direction acts onthe force receiving portions 218 and 219.

When a force +Fz in the positive Z-axis direction acts on the forcereceiving portions 218 and 219 via the force receiving body 260, theforce receiving portions 218 and 219 are displaced in the positiveZ-axis direction, as shown in FIG. 13. Because of this, each of thefirst through fourth deformable elements 210A through 210D is subjectedto upward force like the upward force shown in FIG. 6. In this case, thefirst tilting portion 213A and the third tilting portion 213C tiltclockwise, and therefore, the first beam 221A and the third beam 221Calso tilt clockwise. As a result, the 1-1st displacement portion D11 andthe 3-1st displacement portion D31 are displaced in the positive Z-axisdirection, and the 1-2nd displacement portion D12 and the 3-2nddisplacement portion D32 are displaced in the negative Z-axis direction.

Meanwhile, the second tilting portion 213B and the fourth tiltingportion 213D tilt counterclockwise, and therefore, the second beam 221Band the fourth beam 221D also tilt counterclockwise. As a result, the2-1st displacement portion D21 and the 4-1st displacement portion D41are displaced in the negative Z-axis direction, and the 2-2nddisplacement portion D22 and the 4-2nd displacement portion D42 aredisplaced in the positive Z-axis direction.

(2-2-4. Where a Moment +Mx is Applied)

FIG. 14 is a diagram for explaining displacements caused in therespective displacement bodies 220A through 220D of the basic structure200 in FIG. 8 when a moment +Mx around the positive X-axis acts on theforce receiving portions 218 and 219. In the present application, thedirection of rotation of a right screw in a case where the right screwis advanced in the positive direction of a predetermined coordinate axisis defined as a positive moment around the coordinate axis.

When a moment +Mx around the positive X-axis acts on the force receivingportions 218 and 219 via the force receiving body 260, the portion ofeach of the force receiving portions 218 and 219 on the positive Y-axisside (the upper side in FIG. 14) is displaced in the positive Z-axisdirection (the front side), and the portion of each of the forcereceiving portions 218 and 219 on the negative Y-axis side (the lowerside in 14) is displaced in the negative Z-axis direction (the backside). That is, a force in the same direction as in FIG. 13 acts on thefirst deformable element 210A and the second deformable element 210B.Therefore, as described in 2-2-3., the 1-1st displacement portion D11 isdisplaced in the positive Z-axis direction, the 1-2nd displacementportion D12 is displaced in the negative Z-axis direction, the 2-1stdisplacement portion D21 is displaced in the negative Z-axis direction,and the 2-2nd displacement portion D22 is displaced in the positiveZ-axis direction.

Meanwhile, the third deformable element 210C is subjected to downwardforce like the downward force shown in FIG. 5 from the force receivingportion 219. In this case, the third tilting portion 213C tiltscounterclockwise, and therefore, the third beam 221C also tiltscounterclockwise. As a result, the 3-1st displacement portion D31 isdisplaced in the negative Z-axis direction, and the 3-2nd displacementportion D32 is displaced in the positive Z-axis direction.

The fourth deformable element 210D is subjected to downward force likethe downward force shown in FIG. 5 from the force receiving portion 218.In this case, the fourth tilting portion 213D tilts clockwise, andtherefore, the fourth beam 221D also tilts clockwise. As a result, the4-1st displacement portion D41 is displaced in the positive Z-axisdirection, and the 4-2nd displacement portion D42 is displaced in thepositive Z-axis direction.

(2-2-5. Where a Moment +My is Applied)

FIG. 15 is a diagram for explaining displacements caused in therespective displacement bodies 220A through 220D of the basic structure200 in FIG. 8 when a moment +My around the positive Y-axis acts on theforce receiving portions 218 and 219.

When a moment +My around the positive Y-axis acts on the force receivingportions 218 and 219 via the force receiving body 260, the forcereceiving portion 218 located on the negative X-axis side is displacedin the positive Z-axis direction (the direction from the front sidetoward the front side in FIG. 15), and the force receiving portion 219located on the positive X-axis side is displaced in the negative Z-axisdirection (the direction from the front side toward the back side inFIG. 15). That is, a force in the same direction as in FIG. 13 acts onthe first deformable element 210A and the fourth deformable element210D. Therefore, as described in 2-2-3., the 1-1st displacement portionD11 is displaced in the positive Z-axis direction, the 1-2nddisplacement portion D12 is displaced in the negative Z-axis direction,the 4-1st displacement portion D41 is displaced in the negative Z-axisdirection, and the 4-2nd displacement portion D42 is displaced in thepositive Z-axis direction.

Meanwhile, as shown in FIG. 15, the second deformable element 210B andthe third deformable element 210C are subjected to force in the negativeZ-axis direction (see FIG. 5). Because of the action of such force, thesecond tilting portion 213B tilts clockwise in the second deformableelement 210B, and therefore, the second beam 221B also tilts clockwise.As a result, the 2-1st displacement portion D21 is displaced in thepositive Z-axis direction, and the 2-2nd displacement portion D22 isdisplaced in the negative Z-axis direction. In the third deformableelement 210C, the third tilting portion 213C tilts counterclockwise, asin FIG. 14. Therefore, the 3-1st displacement portion D31 is displacedin the negative Z-axis direction, and the 3-2nd displacement portion D32is displaced in the positive Z-axis direction.

(2-2-6. Where a Moment +Mz is Applied)

FIG. 16 is a diagram for explaining displacements caused in therespective displacement bodies 220A through 220D of the basic structure200 in FIG. 8 when a moment +Mz around the positive Z-axis acts on theforce receiving portions 218 and 219.

When a moment +Mz around the positive Z-axis acts on the force receivingportions 218 and 219 via the force receiving body 260, the forcereceiving portion 219 located on the negative X-axis side is displacedin the negative Y-axis direction, and the force receiving portion 218located on the positive X-axis side is displaced in the positive Y-axisdirection. Since the displacement of the force receiving portion 218located on the positive X-axis side is in the same direction as in acase where the force +Fy is applied (see FIG. 12), the second deformableelement 210B and the third deformable element 210C disposed on thepositive X-axis side have the same elastic deformation as that in FIG.12. That is, the 2-1st displacement portion D21 is displaced in thepositive Z-axis direction, the 2-2nd displacement portion D22 isdisplaced in the negative Z-axis direction, the 3-1st displacementportion D31 is displaced in the positive Z-axis direction, and the 3-2nddisplacement portion D32 is displaced in the negative Z-axis direction.

Meanwhile, the first deformable element 210A is subjected to tensileforce like the tensile force shown in FIG. 4, due to the displacement ofthe force receiving portion 219 in the negative Y-axis direction. Inthis case, the first tilting portion 213A and the first beam 221A tiltclockwise. Therefore, the 1-1st displacement portion D11 is displaced inthe positive Z-axis direction, and the 1-2nd displacement portion D12 isdisplaced in the negative Z-axis direction.

Further, the fourth deformable element 210D is subjected to compressiveforce like the compressive force shown in FIG. 3, due to thedisplacement of the force receiving portion 219 in the negative Y-axisdirection. In this case, the fourth tilting portion 213D and the fourthbeam 221D tilt clockwise. Therefore, the 4-1st displacement portion D41is displaced in the positive Z-axis direction, and the 4-2nddisplacement portion D42 is displaced in the negative Z-axis direction.

As a summary of the above description, FIG. 17 shows a list of thedirections of the tilting movements caused in the respective tiltingportions 213A through 213D of the basic structure 200 in FIG. 8 and thedisplacements caused in the respective displacement portions D11 throughD42 of the displacement bodies 220A through 220D in a case where theforces +Fx, +Fy, and +Fz in the respective axis directions of the X-YZthree-dimensional coordinate system, and the moments +Mx, +My, and +Mzaround the respective axes act on the force receiving portions 218 and219. In FIG. 17, the directions of rotation (clockwise/counterclockwise)shown in the columns for the respective tilting portions 213A through213D are the directions observed from the origin O. Further, the symbol“+” written in the columns for the respective displacement portions D11through D42 means that the distance between the correspondingdisplacement portion and the support 250 increases, and the symbol “−”means that the distance between the corresponding displacement portionand the support 250 decreases.

In a case where the forces and moments acting on the force receivingbody 260 are in negative directions and in negative rotative directions,the directions of the tilting movements of the tilting portions 213Athrough 213D are all reversed from those in the above described cases.As a result, the directions of displacements caused in the displacementportions D11 through D42 of the respective displacement bodies 220Athrough 220D are also reversed, and the directions of the tiltingmovements and the increases/decreases (+/−) in the distance between therespective displacement portions D11 through D42 and the support 250 areall reversed from those shown in the list in FIG. 17.

<2-3. Structure of a Force Sensor>

Next, the structure of the force sensor 200 c including the basicstructure 200 described above in 2-1 and 2-2 is described.

FIG. 18 is a schematic top view of an example of the force sensor 200 cthat adopts the basic structure 200 shown in FIG. 8. FIG. 19 is aschematic front view of the force sensor 200 c of FIG. 18, as viewedfrom the positive Y-axis side.

As shown in FIGS. 18 and 19, the force sensor 200 c includes the abovedescribed basic structure 200 and a detection circuit 240 that detectsan applied force and an applied moment in accordance with displacementscaused in the respective displacement portions D11 through D42 of thedisplacement bodies 220A through 220D of the basic structure 200. Asshown in FIGS. 18 and 19, the detection circuit 240 of this embodimentincludes: eight capacitive elements C11 through C42 disposed one by onein the respective displacement portions D11 through D42 of thedisplacement bodies 220A through 220D; and a measuring unit 241 that isconnected to these capacitive elements C11 through C42, and measures theapplied force in accordance with changes in the capacitance values ofthe capacitive elements C11 through C42.

The specific configurations of the eight capacitive elements C11 throughC42 are as follows. Specifically, as shown in FIG. 19, the 1-1stcapacitive element C11 includes: a 1-1st displacement electrode Em11disposed on the 1-1st displacement portion D11 of the first beam 221Avia an insulator (not shown); and a 1-1st fixed electrode Ef11 disposedon the support 250 via an insulator (not shown) in such a manner as toface the 1-1st displacement electrode Em11. Also, the 1-2nd capacitiveelement C12 includes: a 1-2nd displacement electrode Em12 disposed onthe 1-2nd displacement portion D12 of the first beam 221A via aninsulator (not shown); and a 1-2nd fixed electrode Ef12 disposed on thesupport 250 via an insulator (not shown) in such a manner as to face the1-2nd displacement electrode Em12.

Likewise, as shown in FIG. 19, the 2-1st capacitive element C21includes: a 2-1st displacement electrode Em21 disposed on the 2-1stdisplacement portion D21 of the second beam 221B via an insulator (notshown); and a 2-1st fixed electrode Ef21 disposed on the support 250 viaan insulator (not shown) in such a manner as to face the 2-1stdisplacement electrode Em21. The 2-2nd capacitive element C22 includes:a 2-2nd displacement electrode Em22 disposed on the 2-2nd displacementportion D22 of the second beam 221B via an insulator (not shown); and a2-2nd fixed electrode Ef22 disposed on the support 250 via an insulator(not shown) in such a manner as to face the 2-2nd displacement electrodeEm22.

Further, although not shown in the drawing, the 3-1st capacitive elementC31 includes: a 3-1st displacement electrode Em31 disposed on the 3-1stdisplacement portion D31 of the third beam 221C via an insulator; and a3-1st fixed electrode Ef31 disposed on the support 250 via an insulatorin such a manner as to face the 3-1st displacement electrode Em31. The3-2nd capacitive element C32 includes: a 3-2nd displacement electrodeEm32 disposed on the 3-2nd displacement portion D32 of the third beam221C via an insulator; and a 3-2nd fixed electrode Ef32 disposed on thesupport 250 via an insulator in such a manner as to face the 3-2nddisplacement electrode Em32.

Likewise, the 4-1st capacitive element C41 includes: a 4-1stdisplacement electrode Em41 disposed on the 4-1st displacement portionD41 of the fourth beam 221D via an insulator; and a 4-1st fixedelectrode Ef41 disposed on the support 250 via an insulator in such amanner as to face the 4-1st displacement electrode Em41. The 4-2ndcapacitive element C42 includes: a 4-2nd displacement electrode Em42disposed on the 4-2nd displacement portion D42 of the fourth beam 221Dvia an insulator; and a 4-2nd fixed electrode Ef42 disposed on thesupport 250 via an insulator in such a manner as to face the 4-2nddisplacement electrode Em42.

Although not clearly shown in FIGS. 18 and 19, these capacitive elementsC11 through C42 are connected to the measuring unit 241 by apredetermined circuit, and the capacitance values of the capacitiveelements C11 through C42 are supplied to the measuring unit 241.

<2-4. Operation of the Force Sensor>

Next, operation of the force sensor 200 c described in 2-3. isdescribed.

(2-4-1. Where a Force +Fx in the Positive X-Axis Direction is Applied)

When a force +Fx in the positive X-axis direction acts on the forcereceiving portions 218 and 219 of the force sensor 200 c via the forcereceiving body 260, the distance between the 1-1st displacementelectrode Em11 and the 1-1st fixed electrode Ef11 decreases in the 1-1stcapacitive element C11, but the distance between the 1-2nd displacementelectrode Em12 and the 1-2nd fixed electrode Ef12 increases in the 1-2ndcapacitive element C12, as shown in FIG. 17. That is, the capacitancevalue of the 1-1st capacitive element C11 increases, and the capacitancevalue of the 1-2nd capacitive element C12 decreases. Likewise, thecapacitance value of the 2-1st capacitive element C21 increases, and thecapacitance value of the 2-2nd capacitive element C22 decreases, as canbe seen from FIG. 17. The capacitance value of the 3-1st capacitiveelement C31 decreases, and the capacitance value of the 3-2nd capacitiveelement C32 increases.

Further, the capacitance value of the 4-1st capacitive element C41decreases, and the capacitance value of the 4-2nd capacitive element C42increases.

FIG. 20 is a table as a list that shows the increases/decreases in thecapacitance values of the respective capacitive elements in a case wherethe forces +Fx, +Fy, and +Fz in the respective axis directions or themoments +Mx, +My, and +Mz around the respective axes in the X-Y-Zthree-dimensional coordinate system act on the force receiving portions218 and 219. The increases/decreases in the capacitance values of theabove described capacitive elements C11 through C42 are summarized inthe column for Fx in FIG. 20. In the list, each symbol “+” indicatesthat the capacitance value increases, and each symbol “−” indicates thatthe capacitance value decreases.

In this embodiment, in the respective beams 221A through 221D, the firstdisplacement portions D11, D21, D31, and D41, and the seconddisplacement portions D12, D22, D32, and D42 are arranged at equaldistances from the centers of the tilting movements of the correspondingbeams 221A through 221D. Accordingly, in the respective beams 221Athrough 221D, the magnitudes (|ΔC11|, |ΔC21|, |ΔC31|, and |ΔC41|) of thechanges in the capacitance values of the capacitive elements C11, C21,C31, and C41 disposed in the first displacement portions D11, D21, D31,and D41 are equal to the magnitudes (|ΔC12|, |ΔC22|, |ΔC32|, and |ΔC42|)of the changes in the capacitance values of the capacitive elements C12,C22, C32, and C42 disposed in the second displacement portions D12, D22,D32, and D42. Because of this, where|ΔC11|=|ΔC12|=|ΔC21|=|ΔC22|=|ΔC31|ΔC32|=|C41|=|C42|=ΔC, the respectivecapacitance values C11 a through C42 a of the 1-1st through 4-2ndcapacitive elements C11 through C42 when the force +Fx is applied areexpressed by the following [Expression 7].C11a=C11+ΔCC12a=C12−ΔCC21a=C21+ΔCC22a=C22−ΔCC31a=C31−ΔCC32a=C32+ΔCC41a=C41−ΔCC42a=C42+ΔC  [Expression 7]

In accordance with such changes in the capacitance values, the measuringunit 241 measures the applied force +Fx by using the following[Expression 8].+Fx=C11−C12+C21−C22−C31+C32−C41+C42  [Expression 8]

(2-4-2. Where a Force +Fy in the Positive Y-Axis Direction is Applied)

When a force +Fy in the positive Y-axis direction acts on the forcereceiving portions 218 and 219 of the force sensor 200 c via the forcereceiving body 260, the capacitance value of the 1-1st capacitiveelement C11 increases, the capacitance value of the 1-2nd capacitiveelement C12 decreases, the capacitance value of the 2-1st capacitiveelement C21 decreases, and the capacitance value of the 2-2nd capacitiveelement C22 increases, as can be seen from FIG. 17. Further, thecapacitance value of the 3-1st capacitive element C31 decreases, thecapacitance value of the 3-2nd capacitive element C32 increases, thecapacitance value of the 4-1st capacitive element C41 increases, and thecapacitance value of the 4-2nd capacitive element C42 decreases. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C42 are summarized in the column for Fy in FIG. 20.

In this case, in the respective beams 221A through 221D, the magnitudesof the changes in the capacitance values of the capacitive elements C11,C21, C31, and C41 disposed in the first displacement portions D11, D21,D31, and D41 can also be regarded as equal to the magnitudes of thechanges in the capacitance values of the capacitive elements C12, C22,C32, and C42 disposed in the second displacement portions D12, D22, D32,and D42. Accordingly, taking into account the changes in the capacitancevalues of the respective capacitive elements C11 through C42 in the samemanner as in the above [Expression 7], the measuring unit 241 measuresthe applied force +Fy according to the following [Expression 9],+Fy=C11−C12−C21+C22−C31+C32+C41−C42  [Expression 9]

(2-4-3. Where a Force +Fz in the Positive Z-Axis Direction is Applied)

When a force +Fz in the positive Z-axis direction acts on the forcereceiving portions 218 and 219 of the force sensor 200 c via the forcereceiving body 260, the capacitance value of the 1-1st capacitiveelement C11 decreases, the capacitance value of the 1-2nd capacitiveelement C12 increases, the capacitance value of the 2-1st capacitiveelement C21 increases, and the capacitance value of the 2-2nd capacitiveelement C22 decreases, as can be seen from FIG. 17. Further, thecapacitance value of the 3-1st capacitive element C31 decreases, thecapacitance value of the 3-2nd capacitive element C32 increases, thecapacitance value of the 4-1st capacitive element C41 increases, and thecapacitance value of the 4-2nd capacitive element C42 decreases. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C42 are summarized in the column for Fz in FIG. 20.

More specifically, when the force +Fz is applied, the respective tiltingportions 213A through 213D are displaced in the positive Z-axisdirection in total. Therefore, the displacement caused in the 1-1stdisplacement portion D11 is the sum of the overall displacement of thefirst tilting portion 213A in the positive Z-axis direction and thedisplacement in the positive Z-axis direction due to the tiltingmovement of the beam 221A, and the displacement caused in the 1-2nddisplacement portion D12 is the sum of the overall displacement of thetilting portion 213A in the positive Z-axis direction and thedisplacement in the negative Z-axis direction due to the tiltingmovement of the beam 221A. That is, if the changes in the capacitancevalues of the respective capacitive elements C11 and C12 are moreaccurately described, the distance between the 1-1st displacementelectrode Em11 and the 1-1st fixed electrode Ef11 greatly increases bythe amount equivalent to the overall displacement of the first tiltingportion 213A in the positive Z-axis direction. In the 1-2nd capacitiveelement C12, on the other hand, the displacement due to the tiltingmovement of the first beam 221A is offset by the overall displacement ofthe first tilting portion 213A in the positive Z-axis direction, andtherefore, the distance between the 1-2nd displacement electrode Em12and the 1-2nd fixed electrode Ef12 slightly increases. The overallinfluence of the displacements of the tilting portions 213A through 213Din the positive Z-axis direction is also seen in the remainingcapacitive elements C21 to C42.

However, for simplicity, the length of the respective beams 221A through221D in the Z-axis direction is sufficiently greater than the length(height) of the respective tilting portions 213A through 221D in theZ-axis direction in this example. In view of this, the magnitudes(|ΔC11|, |ΔC21|, |ΔC31|, and |ΔC41|) of the changes in the capacitancevalues of the capacitive elements C11, C21, C31, and C41 provided in thefirst displacement portions D11, D21, D31, and D41 of the respectivebeams 221A through 221D can be regarded as equal to the magnitudes(|ΔC12|, |ΔC22|, |ΔC32|, and |ΔC42|) of the changes in the capacitancevalues of the capacitive elements C12, C22, C32, and C42 provided in thesecond displacement portions D12, D22, D32, and D42.

Accordingly, taking into account the changes in the capacitance valuesof the respective capacitive elements C11 through C42 in the same manneras in the above [Expression 7], the measuring unit 241 measures theapplied force +Fz according to the following [Expression 10].+Fz=−C11+C12+C21−C22−C31+C32+C41−C42  [Expression 10]

(2-4-4. Where a Moment +Mx around the Positive X-Axis is Applied)

When a moment +Mx around the positive X-axis acts on the force receivingportions 218 and 219 of the force sensor 200 c via the force receivingbody 260, the capacitance value of the 1-1st capacitive element C11decreases, the capacitance value of the 1-2nd capacitive element C12increases, the capacitance value of the 2-1st capacitive element C21increases, and the capacitance value of the 2-2nd capacitive element C22decreases, as can be seen from FIG. 17.

Further, the capacitance value of the 3-1st capacitive element C31increases, the capacitance value of the 3-2nd capacitive element C32decreases, the capacitance value of the 4-1st capacitive element C41decreases, and the capacitance value of the 4-2nd capacitive element C42increases. The increases/decreases in the capacitance values of thesecapacitive elements C11 through C42 are summarized in the column for Mxin FIG. 20.

In this case, the respective tilting portions 213A through 213D aredisplaced in the Z-axis direction in total, as in the case where theforce +Fz in the positive Z-axis direction is applied. Therefore, to beprecise, it is necessary to take into account the displacements of thetilting portions 213A through 213D in evaluating the displacements ofthe respective displacement portions D11 through D42. However, thelength of the respective beams 221A through 221D in the Z-axis directionis sufficiently greater than the length (height) of the respectivetilting portions 213A through 221D in the Z-axis direction, as describedabove. Because of this, the overall displacements of the respectivetilting portions 213A through 213D in the Z-axis direction can beignored. That is, in this case, the magnitudes of the changes in thecapacitance values of the capacitive elements C11, C21, C31, and C41disposed in the displacement portions D11, D21, D31, and D41 of therespective beams 221A through 221D can also be regarded as equal to themagnitudes of the changes in the capacitance values of the capacitiveelements C12, C22, C32, and C42 disposed in the other displacementportions D12, D22, D32, and D42. This also applies in the laterdescribed case where a moment +My around the positive Y-axis is applied.

Accordingly, taking into account the changes in the capacitance valuesof the respective capacitive elements C11 through C42 in the same manneras in the above [Expression 7], the measuring unit 241 measures theapplied moment +Mx according to the following [Expression 11].+Mx=−C11+C12+C21−C22+C31−C32−C41+C42  [Expression 11]

(2-4-5. Where a Moment +My Around the Positive Y-Axis is Applied)

When a moment +My around the positive Y-axis acts on the force receivingportions 218 and 219 of the force sensor 200 c via the force receivingbody 260, the capacitance value of the 1-1st capacitive element C11decreases, the capacitance value of the 1-2nd capacitive element C12increases, the capacitance value of the 2-1st capacitive element C21decreases, and the capacitance value of the 2-2nd capacitive element C22increases, as can be seen from FIG. 17.

Further, the capacitance value of the 3-1st capacitive element C31increases, the capacitance value of the 3-2nd capacitive element C32decreases, the capacitance value of the 4-1st capacitive element C41increases, and the capacitance value of the 4-2nd capacitive element C42decreases. The increases/decreases in the capacitance values of thesecapacitive elements C11 through C42 are summarized in the column for Myin FIG. 20.

Accordingly, taking into account the changes in the capacitance valuesof the respective capacitive elements C11 through C42 in the same manneras in the above [Expression 7], the measuring unit 241 measures theapplied moment +My according to the following [Expression 12].+My=−C11+C12−C21+C22+C31−C32+C41−C42  [Expression 12]

(2-4-6. Where a Moment +Mz around the Positive Z-Axis is Applied)

When a moment +Mz around the positive Z-axis acts on the force receivingportions 218 and 219 of the force sensor 200 c via the force receivingbody 260, the capacitance value of the 1-1st capacitive element C11decreases, the capacitance value of the 1-2nd capacitive element C12increases, the capacitance value of the 2-1st capacitive element C21decreases, and the capacitance value of the 2-2nd capacitive element C22increases, as can be seen from FIG. 17.

Further, the capacitance value of the 3-1st capacitive element C31decreases, the capacitance value of the 3-2nd capacitive element C32increases, the capacitance value of the 4-1st capacitive element C41decreases, and the capacitance value of the 4-2nd capacitive element C42increases. The increases/decreases in the capacitance values of thesecapacitive elements C11 through C42 are summarized in the column for Mzin FIG. 20.

Accordingly, taking into account the changes in the capacitance valuesof the respective capacitive elements C11 through C42 in the same manneras in the above [Expression 7], the measuring unit 241 measures theapplied moment +Mz according to the following [Expression 13].+Mz=−C11+C12−C21+C22−C31+C32−C41+C42  [Expression 13]

It should be noted that, in cases where the negative forces −Fx, −Fy,and −Fz in the respective axis directions or the moments −Mx, −My, and−Mz around the respective negative axes act on the force receiving body260 of the force sensor 200 c, the increases/decreases in the distancesbetween the electrodes of the respective capacitive elements C11 throughC42 are reversed from those shown in FIG. 17, as described above.Therefore, to detect the forces −Fx, −Fy, and −Fz or the moments −Mx,−My, and −Mz, the signs of C11 through C42 in the right sides of[Expression 8] through [Expression 13] should be reversed.

<2-5. Other-Axis Sensitivity of the Force Sensor>

Referring now to FIG. 21, the other-axis sensitivity of the force sensor200 c according to this embodiment is described. FIG. 21 is a table as alist that shows the other-axis sensitivities VFx through VMz of theforces Fx, Fy, and Fz in the respective axis directions and the momentsMx, My, and Mz around the respective axes in the force sensor 200 cshown in FIG. 18.

For ease of explanation, [Expression 8] through [Expression 13] arecollectively shown below in [Expression 14]. In [Expression 14], thesymbol “+” indicating that the force or the moment is positive is notshown.

[Expression 14]Fx=C11+C12+C21−C22−C31+C32−C41+C42  Expression 8:Fy=C11−C12−C21+C22−C31+C32+C41−C42  Expression 9:Fz=−C11−C12−C12+C21−C22−C31+C32+C41−C42  Expression 10:Mx=−C11+C12+C21−C22+C31−C32−C41+C42  Expression 11:My=−C11+C12−C21+C22+C31−C32+C41−C42  Expression 12:Mz=−C+C12−C21+C22−C31+C32−C41+C42  Expression 13:

The numbers shown in the table in FIG. 21 are values obtained byassigning the respective forces Fx, Fy, and Fz and the respectivemoments Mx, My, and Mz in the table shown in FIG. 20 to the respectiveright sides of the above [Expression 14] ([Expression 8] through[Expression 13]). Each capacitive element with the symbol “+” isrepresented by +1, and each capacitive element with the symbol “−” isrepresented by −1. That is, the number “8” shown in the cell where thecolumn Fx and the row VFx intersect is the value obtained according toC11=C21=C32=C42=+1, and C12=C22=C31=C41=−1, which are based on the rowfor Fx in FIG. 20, in the expression for Fx ([Expression 8]). Also, thenumber “0” shown in the cell where the column Fx and the row VFyintersect is the value obtained according to C11=C22=C32=C41=+1, andC12=C21=C31=C42=−1, which are based on the row for Fy in FIG. 20, in theexpression for Fx ([Expression 8]). The same applies to the numbersshown in the other cells.

According to FIG. 21, the other-axis sensitivities of Fx and My, and theother-axis sensitivities of Fy and Mx are 100%. Certainly, the signs ofthe right sides of [Expression 8] and [Expression 12] are the opposite,and the signs of the right sides of [Expression 9] and [Expression 11]are the opposite. Therefore, the force sensor 200 c according to thisembodiment cannot distinguish between Fx and My, and cannot distinguishbetween Fy and Mx, either. That is, the force sensor 200 c cannot detectall the forces Fx, Fy, and Fz in the respective axis directions, and themoments Mx, My, and Mz around the respective axes. However, the forcesensor 200 c can be effectively used by limiting the use of the forcesensor 200 c to usage in which Fx and Fy are not applied or usage inwhich Mx and My are not applied.

According to this embodiment described above, displacements caused inthe tilting portions 213A through 213D can be easily amplified by theactions of the beams 221A through 221D that are displaced by the tiltingmovements of the tilting portions 213A through 213D. Further, with theuse of the 1-1st through 4-2nd capacitive elements C11 through C42, fourcomponents can be detected from among applied forces Fx, Fy, and Fz andapplied moments Mx, My, and Mz, in accordance with the differencesbetween changes in the capacitance values of these capacitive elementsC11 through C42. That is, this embodiment can provide the force sensor200 c that is inexpensive but highly sensitive, and is hardly affectedby temperature changes or in-phase noise in the use environment, becauseall the components of Fx through Mz calculated according to [Expression8] through [Expression 13] are detected in accordance with differences.

Further, the displacement bodies 220A through 220D include connectingbodies 222A through 222D connecting the corresponding tilting portions213A through 213D and the beams 221A through 221D, respectively, and thefirst displacement portions D11, D21, D31, and D41 and the seconddisplacement portions D12, D22, D32, and D42 of the displacement bodies220A through 220D are arranged symmetrically with respect to theconnecting portions between the connecting bodies 222A through 222D andthe corresponding beams 221A through 221D. Because of this, thedisplacements caused in the first displacement portions D11, D21, D31,and D41 and the displacements caused in the second displacement portionsD12, D22, D32, and D42 are of the same magnitude but have differentsigns from each other, Thus, applied forces and moments can be detectedthrough simple calculations.

The force sensor 200 c also includes: the force receiving body 260 thatis connected to the two force receiving portions 218 and 219 of thedeformable body 210, and receives the applied forces Fx, Fy, and Fz andthe moments Mx, My, and Mz; and the support 250 that is disposed to facethe displacement bodies 220A through 220D, and is connected to the twofixed portions 216 and 217 of the deformable body 210. With thisarrangement, it is possible to transmit the applied forces Fx, Fy, andFz and the moments Mx, My, and Mz to the deformable body 210 withoutfail.

Further, the deformable body 210 has a ring-like shape, the two forcereceiving portions 218 and 219 are positioned symmetrically with respectto the origin O on the X-axis, and the two fixed portions 216 and 217are positioned symmetrically with respect to the origin O on the Y-axis.With this arrangement, calculations for detecting the applied forces Fx,Fy, and Fz, and the moments Mx, My, and Mz are easy.

§ 3. Force Sensor According to a Third Embodiment of the PresentInvention and Modifications Thereof 3-1. Force Sensor According to aThird Embodiment of the Present Invention

The force sensor 200 c described in § 2 is capable of detecting fourcomponents from among the forces Fx, Fy, and Fz and moments Mx, My, andMz in the respective axis directions. However, to detect these fourcomponents, it is not always necessary, to provide eight capacitiveelements in a force sensor. In the description below, a force sensorcapable of detecting four components with fewer capacitive elementsaccording to a third embodiment will be described as a modification ofthe above described force sensor 200 c.

FIG. 22 is a schematic top view of a force sensor 300 c according to thethird embodiment of the present invention.

As shown in FIG. 22, the force sensor 300 c differs from the forcesensor 200 c according to the second embodiment in that beams 321Athrough 321D are designed as cantilever beams. Specifically, the beams321A through 321D of the force sensor 300 c each has a cantileverstructure in which the top end portion in the clockwise direction inFIG. 18 is eliminated from each of the beams 221A through 221D of theforce sensor 200 c. Therefore, in the force sensor 300 c, displacementportions D11, D21, D31, and D41 are formed in the beams 321A through321D, respectively. Capacitive elements C11, C12, C31, and C41 areprovided in the four displacement portions D11, D21, D31, and D41,respectively. The configuration of each of the capacitive elements C11through C41 is the same as that of the second embodiment.

Although not shown in FIG. 22, the four capacitive elements C11 throughC41 are connected to a measuring unit 341 of a detection circuit 340 bya predetermined circuit, and the capacitance values of the capacitiveelements C11 through C41 are supplied to the measuring unit 341. Asdescribed later, the measuring unit 341 detects the force acting on theforce sensor 300 c, in accordance with changes in the capacitance valuesof the respective capacitive elements C11 through C41.

The other aspects of the force sensor 300 c are the same as those of thesecond embodiment, Therefore, the same components as those of the secondembodiment are denoted by substantially the same reference numerals asthose used in the second embodiment, and detailed explanation thereof isnot made herein.

Next, operation of the force sensor 300 c according to this embodimentare described. The following is a description of a case where fourcomponents Fz, Mx, My, and Mz are detected from among forces Fx, Fy, andFz in the respective axis directions and moments Mx, My, and Mz aroundthe respective axes in the X-Y-Z three-dimensional coordinate system. Itshould be noted that these four components are four components the forcesensor 200 c according to the second embodiment can also detect.

As described above, the force sensor 300 c according to this embodimenthas substantially the same structure as the force sensor 200 c accordingto the second embodiment, except that the beams 321A through 321D aredesigned as cantilever beams. Accordingly, when a force or a moment actson force receiving portions 318 and 319 via a force receiving body 360,the detection portions D11, D21, D31, and D41 of the respective beams321A through 321D have the same displacements as those of thecorresponding detection portions D11, D21, D31, and D41 of the forcesensor 200 c according to the second embodiment.

Because of the above, when the four components Fz, Mx, My, and Mz of theforces and the moments act on the force sensor 300 c, the capacitancevalues of the capacitive elements C11 through C41 change as shown in alist in FIG. 23. In the list, each symbol “+” indicates that thecapacitance value increases, and each symbol “−” indicates that thecapacitance value decreases, as in FIG. 20. In the table shown in FIG.23, the increases/decreases in the capacitance values of the fourcapacitive elements C11, C21, C31, C41 are the same as those observedwhen the force Fz and the moments Mx, My, and Mz in FIG. 20 are applied.

In accordance with such changes in the capacitance values, the measuringunit 341 measures the applied force Fz and the moments Mx, My, and Mzaccording to [Expression 15] shown below. [Expression 15] is obtained byeliminating C12, C22, C32, and C42 from the expressions of Fz, Mx, My,and Mz in [Expression 14].Fz=−C11+C21−C31+C41Mx=−C11+C21+C31−C41My=−C11−C21+C31+C41Mz=−C11−C21−C31−C41  [Expression 15]

Where the other-axis sensitivities of the force Fz and the moments Mx,My, and Mz are calculated according to [Expression 15], the results areas shown in FIG. 24. The other-axis sensitivities are values obtained byassigning the force Fz and the moments Mx, My, and Mz in the table shownin FIG. 23 to the respective right sides of the above [Expression 15].Each capacitive element with the symbol “+” is represented by +1, andeach capacitive element with the symbol “−” is represented by −1, as inFIG. 21. As shown in FIG. 24, the other-axis sensitivities of the forceFz and the moments Mx, My, and Mz are zero. However, according to[Expression 15], the moment Mz around the Z-axis is obtained as the stunof C11 through C41. Therefore, it is necessary to pay attention to thepoint that the moment Mz is easily affected by temperature changes andin-phase noise in the use environment of the force sensor 300 c.

According to this embodiment described above, displacements caused inthe tilting portions 313A through 313D can be easily amplified by theactions of the beams 321A through 321D that are displaced by the tiltingmovements of the tilting portions 313A through 313D. Further, except forthe moment Mz around the Z-axis, the applied force Fz and the moments Mxand My can be detected in accordance with the differences betweenchanges in the capacitance values of the four capacitive elements C11through C41. That is, this embodiment can provide the force sensor 300 cthat is inexpensive but highly sensitive, and is hardly affected bytemperature changes or in-phase noise in the use environment withrespect to the force Fz and the moments Mx and My.

The force sensor 300 c also includes: the force receiving body 360 thatis connected to the two force receiving portions 318 and 319 of adeformable body 310, and receives the applied force Fz and the momentsMx, My, and Mz; and a fixed body 350 that is disposed to face respectivedisplacement bodies 320A through 320D, and is connected to two fixedportions 316 and 317 of the deformable body 310. With this arrangement,it is possible to transmit the applied force Fz and the moments Mx, My,and Mz to the deformable body 310 without fail.

Further, the deformable body 310 has a ring-like shape, the two forcereceiving portions 318 and 319 are positioned symmetrically with respectto the origin O on the X-axis, and the two fixed portions 316 and 317are positioned symmetrically with respect to the origin O on the Y-axis.With this arrangement, calculations for detecting the applied force Fzand the moments Mx, My, and Mz are easy.

3-2. Force Sensor According to a Modification

As described above, when measuring the moment Mz around the Z-axis, theforce sensor 300 c is easily affected by temperature changes or in-phasenoise in the use environment. Therefore, it is more preferable for aforce sensor to be less affected by those factors when measuring themoment Mz. The following is a description of a force sensor as amodification that has six capacitive elements.

FIG. 25 is a schematic top view of a force sensor 301 c according to amodification of the third embodiment.

As shown in FIG. 25, the force sensor 301 c differs from the forcesensor 200 c according to the second embodiment in that first and secondbeams 321A and 321B are designed as cantilever beams. Specifically, thefirst and second beams 321A and 321B of the force sensor 301 c accordingto this modification are the same as the first and second beams 321A and321B of the force sensor 300 c according to the third embodiment, andthird and fourth beams 321C and 321D of the force sensor 301 c are thesame as the third and fourth beams 221C and 221D of the force sensor 200c according to the second embodiment shown in FIG. 18. Therefore, in theforce sensor 301 c, a 1-1st displacement portion D11 is formed in thefirst beam 321A, a 2-1st displacement portion D21 is formed in thesecond beam 321B, a 3-1st displacement portion D31 and a 3-2nddisplacement portion D32 are formed in the third beam 321C, and a 4-1stdisplacement portion D41 and a 4-2nd displacement portion D42 are formedin the fourth beam 321D. The layout of the 3-1st displacement portionD31, the 3-2nd displacement portion D32, the 4-1st displacement portionD41, and the 4-2nd displacement portion D42 is identical to the layoutof the displacement portions D31 through D42 of the force sensor 200 caccording to the second embodiment. Capacitive elements C11, C21, C31,C32, C41, and C42 are provided in the six displacement portions D11,D21, D31, D32, D41, and D42, respectively. The configuration of each ofthe capacitive elements is the same as that of the second embodiment.

Although not clearly shown in FIG. 25, these six capacitive elementsC11, C21, C31, C32, C41, and C42 are connected to a measuring unit 341by a predetermined circuit, and the capacitance values of the respectivecapacitive elements are supplied to the measuring unit 341. As describedlater, the measuring unit 341 detects the force acting on the forcesensor 301 c, in accordance with changes in the capacitance values ofthe respective capacitive elements.

The other aspects of the force sensor 301 c are the same as those of thesecond embodiment. Therefore, the same components as those of the secondembodiment are denoted by substantially the same reference numerals asthose used in the second embodiment, and detailed explanation thereof isnot made herein.

Next, operation of the force sensor 301 c according to this embodimentis described. The following is a description of a case where fourcomponents Fz, Mx, My, and Mz are detected from among forces Fx, Fy, andFz in the respective axis directions and moments Mx, My, and Mz aroundthe respective axes in the X-Y-Z three-dimensional coordinate system, asin the third embodiment.

When a force or a moment acts on the force receiving portions 318 and319 via the force receiving body 360 of the force sensor 301 c accordingto this embodiment, the six detection portions D11, D21, D31, D32, D41,and D42 have the same displacements as those of the correspondingdetection portions D11, D21, D31, D32, D41, and D42 of the force sensor200 c according to the second embodiment.

Therefore, when a force and moments act on the force sensor 301 c, thecapacitance value of each capacitive element changes like thecapacitance value of each corresponding capacitive element shown in FIG.20. In accordance with such changes in the capacitance values, themeasuring unit 341 measures the applied force Fz and the moments Mx, My,and Mz according to [Expression 16] shown below. Of the four expressionsshown in [Expression 16], the expressions of Fz, Mx, and My areidentical to the corresponding expressions in [Expression 15]. In[Expression 16], all the other-axis sensitivities of the force Fz andthe moments Mx, My, and Mz are of course zero.Fz=−C11+C21−C31+C41Mx=−C11+C21+C31−C41My=−C11−C21+C31±C41Mz=−C11−C21+C32+C42  [Expression 16]

According to this embodiment described above, the effects described inthe third embodiment can be achieved, and further, the moment Mz aroundthe Z-axis can be calculated in accordance with differences. Thus, theinfluence of temperature changes and in-phase noise in the useenvironment of the force sensor 301 c can be eliminated, and the momentMz can be measured with high precision.

3-3. Force Sensors According to Further Modifications

(3-3-1, Modification 1)

Although a force sensor from which the four capacitive elements C12,C22, C32, and C42 are eliminated is shown as the force sensor 300 c fordetecting the force Fz and the moments Mx, My, and Mz in FIG. 22, thisembodiment is not limited to such a mode. Another example of a forcesensor may exclude the four capacitive elements C11, C22, C31, and C42.That is, this force sensor has the four capacitive elements C12, C21,C32, and C41.

The increases/decreases in the respective capacitive elements C12, C21,C32, and C41 when the force and the moments act on the force sensor areidentical to the increases/decreases in the capacitive elements C12,C21, C32, and C41 shown in FIG. 20. Accordingly, the measuring unit 341of this force sensor measures the applied force Fz and the moments Mx,My, and Mz according to [Expression 17] shown below. [Expression 17] isobtained by eliminating C11, C22, C31, and C42 from the expressions ofFz, Mx, My, and Mz in [Expression 14].Fz=C12+C21+C32+C41Mx=C12+C21−C32−C41My=C12−C21−C32+C41Mz=C12−C21+C32−C41  [Expression 17]

Where the other-axis sensitivities of the force Fz and the moments Mx,My, and Mz are calculated in accordance with the increases/decreases inthe respective capacitive elements C12, C21, C32, and C41, and[Expression 17], the results are identical to those shown in FIG. 24.Accordingly, the other-axis sensitivities of the force Fz and themoments Mx, My, and Mz are zero. However, according to [Expression 17],the force Fz in the Z-axis direction is obtained in accordance with thesum of C12, C21, C32, and C41. Therefore, it is necessary to payattention to the point that the force Fz is easily affected bytemperature changes and in-phase noise in the use environment of theforce sensor.

(3-3-2. Modification 2)

Alternatively, a force sensor from which the four capacitive elementsC12, C21, C32, and C41 are eliminated may be used as the force sensor300 c for detecting the force Fz and the moments Mx, My, and Mz.

That is, this force sensor has the four capacitive elements C11, C22,C31, and C42.

The increases/decreases in the respective capacitive elements C12, C21,C32, and C41 when the force and the moments act on the force sensor areidentical to the increases/decreases in the capacitive elements C11,C22, C31, and C42 shown in FIG. 20. Accordingly, the measuring unit 341of this force sensor measures the applied force Fz and the moments Mx,My, and Mz according to [Expression 18] shown below. [Expression 18] isthe same as an expression obtained by eliminating C12, C21, C32, and C41from the expressions of Fz, Mx, My, and Mz in [Expression 14].Fz=−C11−C22−C31−C42Mx=−C11−C22+C31+C42My=−C11+C22+C31−C42Mz=−C11+C22−C31+C42  [Expression 18]

Where the other-axis sensitivities of the force Fz and the moments Mx,My, and Mz are calculated in accordance with the increases/decreases inthe respective capacitive elements C11, C22, C31, and C42, and[Expression 18], the results are identical to those shown in FIG. 24.Accordingly, the other-axis sensitivities of the force Fz and themoments Mx, My, and Mz are zero. However, according to [Expression 18],the force Fz in the Z-axis direction is obtained in accordance with thesum of C11, C22, C31, and C42. Therefore, in this modification, it isalso necessary to pay attention to the point that the force Fz, iseasily affected by temperature changes and in-phase noise in the useenvironment of the force sensor.

§ 4. Force Sensor According to a Fourth Embodiment of the PresentInvention and Modifications Thereof 4-1. Force Sensor According to aFourth Embodiment of the Present Invention

In § 3, force sensors that are particularly suitable for measuringmainly the moments Mx, My, and Mz have been described as the thirdembodiment and modifications thereof. The following is a description ofa force sensor according to a fourth embodiment suitable for measuringmainly the forces Fx, Fy, and Fz.

FIG. 26 is a schematic top view of a force sensor 400 c according to thefourth embodiment of the present invention,

The force sensor 400 c according to this embodiment is the same as theforce sensor 300 c of the third embodiment having four capacitiveelements, except for the layout thereof. Specifically, the beams 421Athrough 421D of the force sensor 400 c each has a cantilever structurein which the portion on the side of the fixed portions 216 and 217 iseliminated from each of the beams 221A through 221D of the force sensor200 c. Therefore, in the force sensor 400 c, displacement portions D11,D22, D31, and D42 are formed in the beams 421A through 421D,respectively. Capacitive elements C11, C22, C31, and C42 are provided inthe four displacement portions D11, D22, D31, and D42, respectively. Theconfiguration of each of the capacitive elements is the same as that ofthe second embodiment.

Although not clearly shown in FIG. 26, these four capacitive elementsC11, C22, C31, and C42 are connected to a measuring unit 441 by apredetermined circuit, and the capacitance values of the respectivecapacitive elements are supplied to the measuring unit 441. As describedlater, the measuring unit 441 detects the force acting on the forcesensor 400 c, in accordance with changes in the capacitance values ofthe respective capacitive elements.

The other aspects of the force sensor 400 c are the same as those of thesecond and third embodiments. Therefore, the same components as those ofthe second and third embodiments are denoted by substantially the samereference numerals as those used in the second and third embodiments,and detailed explanation thereof is not made herein.

Next, operation of the force sensor 400 c according to this embodimentis described. The following is a description of a case where fourcomponents Fx, Fy, Fz, and Mz are detected from among forces Fx, Fy, andFz in the respective axis directions and moments Mx, My, and Mz aroundthe respective axes in the X-Y-Z three-dimensional coordinate system. Itshould be noted that these four components are four components the forcesensor 200 c according to the second embodiment can also detect.

FIG. 27 is a table as a list showing changes in the capacitance valuesof the respective capacitive elements in a case where the fourcomponents Fx, Fy, Fz, and Mz of the forces and the moments act on theforce sensor 400 c shown in FIG. 26. As described above, the forcesensor 400 c according to this embodiment has the same structure as theforce sensor 200 c according to the second embodiment, except that thebeams 421A through 421D are designed as cantilever beams. Accordingly,when a force or a moment acts on force receiving portions 418 and 419via a force receiving body 460, the detection portions D11, D22, D31,and D42 of the respective beams 421A through 421D have the samedisplacements as those of the corresponding detection portions D11, D22,D31, and D42, respectively, in the force sensor 200 c according to thesecond embodiment.

Because of the above, when the four components Fx, Fy, Fz, and Mz of theforces and the moments act on the force sensor 400 c, the capacitancevalues of the respective capacitive elements change as shown in a listin FIG. 27. In the list, each symbol “+” indicates that the capacitancevalue increases, and each symbol “−” indicates that the capacitancevalue decreases, as in FIG. 20. In the table shown in FIG. 27, theincreases/decreases in the capacitance values of the four capacitiveelements C11, C22, C31, C42 are identical to those observed when theforces Fx, Fy, and Fz and the moment Mz in FIG. 20 are applied.

In accordance with such changes in the capacitance values, the measuringunit 441 measures the applied forces Fx, Fy, and Fz and the moment Mzaccording to [Expression 19] shown below. [Expression 19] is the same asan expression obtained by eliminating C11, C21, C32, and C41 from theexpressions of Fz, Mx, My, and Mz in [Expression 14].Fx=C11−C22−C31+C42Fy=C11+C22−C31−C42Fz=−C11−C22−C31−C42Mz=−C11+C22−C31+C42  [Expression 19]

Where the other-axis sensitivities of the forces Fx, Fy, and Fz and themoment Mz are calculated according to [Expression 19], the results areall zero as shown in the list in FIG. 24. The method of calculatingother-axis sensitivities is the same as that of the other embodiments.However, according to [Expression 19], the force Fz in the Z-axisdirection is obtained in accordance with the sum of C11, C22, C31, andC42. Therefore, it is necessary to pay attention to the point that theforce Fz is easily affected by temperature changes and in-phase noise inthe use environment of the force sensor 400 c.

According to this embodiment described above, displacements caused inthe tilting portions 413A through 413B can be easily amplified by theactions of the beams 421A through 421D that are displaced by the tiltingmovements of the tilting portions 413A through 413D. Further, except forthe force Fz in the Z-axis direction, the applied forces Fx and Fy, andthe moment Mz can be detected in accordance with the differences betweenchanges in the capacitance values of the four capacitive elements C11,C22, C31, and C42. That is, this embodiment can provide the force sensor400 c that is inexpensive but highly sensitive, and is hardly affectedby temperature changes or in-phase noise in the use environment withrespect to the forces Fx and Fy and the moment Mz.

The force sensor 400 c also includes: the force receiving body 460 thatis connected to the two force receiving portions 418 and 419 of adeformable body 410, and receives the applied forces Fx, Fy, and Fz, andthe moment Mz; and a fixed body 450 that is disposed to face respectivedisplacement bodies 420A through 420D, and is connected to two fixedportions 416 and 417 of the deformable body 410. With this arrangement,it is possible to transmit the applied forces Fx, Fy, and Fz and themoment Mz to the deformable body 410 without fail.

Further, the deformable body 410 has a ring-like shape, the two forcereceiving portions 418 and 419 are positioned symmetrically with respectto the origin O on the X-axis, and the two fixed portions 416 and 417are positioned symmetrically with respect to the origin O on the Y-axis.With this arrangement, calculations for detecting the applied forces Fx,Fy, and Fz and the moment Mz are easy.

4-2. Force Sensor According to a Modification

As described above, when measuring the force Fz in the Z-axis direction,the force sensor 400 c is easily affected by temperature changes orin-phase noise in the use environment. Therefore, it is more preferablefor a force sensor to be less affected by those factors when measuringthe force Fz. The following is a description of a force sensor as amodification that has six capacitive elements.

FIG. 28 is a schematic top view of a force sensor 401 c according to amodification of the fourth embodiment.

As shown in FIG. 28, the force sensor 401 c differs from the forcesensor 200 c according to the second embodiment in that first and secondbeams 421A and 421B are designed as cantilever beams. Specifically, thefirst and second beams 421A and 421B of the force sensor 401 c are thesame as the first and second beams 421A and 421B of the force sensor 400c according to the fourth embodiment, and third and fourth beams 4210and 421D of the force sensor 401 c are the same as the third and fourthbeams 221C and 221D of the force sensor 200 c according to the secondembodiment shown in FIG. 18. Therefore, in the force sensor 401 c, a1-1st displacement portion D11 is formed in the first beam 421A, a 2-2nddisplacement portion D22 is formed in the second beam 421B, a 3-1stdisplacement portion D31 and a 3-2nd displacement portion D32 are formedin the third beam 421C, and a 4-1st displacement portion D41 and a 4-2nddisplacement portion D42 are formed in the fourth beam 421D. The layoutof the 3-1st displacement portion D31, the 3-2nd displacement portionD32, the 4-1st displacement portion D41, and the 4-2nd displacementportion D42 is identical to the layout of the displacement portions D31through D42 of the force sensor 200 c according to the secondembodiment. Capacitive element C11, C22, C31, C32, C41, and C42 areprovided in the six displacement portions D11, D22, D31, D32, D41, andD42, respectively. The configuration of each of the capacitive elementsis the same as that of the second embodiment.

Although not clearly shown in FIG. 28, these six capacitive elementsC11, C22, C31, C32, C41, and C42 are connected to a measuring unit 441by a predetermined circuit, and the capacitance values of the respectivecapacitive elements are supplied to the measuring unit 441. As describedlater, the measuring unit 441 detects the force acting on the forcesensor 401 c, in accordance with changes in the capacitance values ofthe respective capacitive elements.

The other aspects of the force sensor 401 c are the same as those of thesecond embodiment. Therefore, the same components as those of the secondembodiment are denoted by substantially the same reference numerals asthose used in the second embodiment, and detailed explanation thereof isnot made herein.

Next, operation of the force sensor 401 c according to this embodimentis described. The following is a description of a case where fourcomponents Fx, Fy, Fz, and Mz are detected from among forces Fx, Fy, andFz in the respective axis directions and moments Mx, My, and Mz aroundthe respective axes in the X-Y-Z three-dimensional coordinate system, asin the fourth embodiment.

When a force or a moment acts on the force receiving portions 418 and419 via the force receiving body 460 in the force sensor 401 c accordingto this embodiment, the six detection portions D11, D22, D31, D32, D41,and D42 have the same displacements as those of the correspondingdetection portions D11, D22, D31, D32, D41, and D42 of the force sensor200 c according to the second embodiment.

Therefore, when forces and a moment act on the force sensor 401 c, thecapacitance value of each capacitive element changes like thecapacitance value of each corresponding capacitive element shown in FIG.20 (or FIG. 27, as for C11, C22, C31, and C42). In accordance with suchchanges in the capacitance values, the measuring unit 441 measures theapplied forces Fx, Fy, and Fz and the moment Mz according to [Expression20] shown below. Of the four expressions shown in [Expression 20], theexpressions of Fx, Fy, and Mz are identical to the correspondingexpressions in [Expression 19]. In [Expression 20], all the other-axissensitivities of the force Fx, Fz and the moment Mz are of course zero.Fx=C11−C22−C31+C42Fy=C11+C22−C31−C42Fz=−C11−C22+C32+C41Mz=−C11+C22−C31+C42  [Expression 20]

According to this embodiment described above, the effects described inthe fourth embodiment can be achieved, and further, the force Fz in theZ-axis direction can be calculated in accordance with differences. Thus,the influence of temperature changes and in-phase noise in the useenvironment of the force sensor 401 c can be eliminated, and the forceFz can be measured with high precision.

As described above in § 3 and § 4, four force sensors 100 c shown inFIG. 1 are arranged in a closed-loop form so that four components (theset of Fz, Mx, My, and Mz, or the set of Fx, Fy, Fz, and Mz) of forcescan be detected. It is of course also possible to detect only anydesired component(s) from among the four components.

The force sensors 300 c, 301 c, 400 c, and 401 c according to therespective embodiments and their modifications described in § 3 and § 4have been explained as models in which specific beams are replaced withcantilever structures. However, the present invention is not limited tosuch examples. While the doubly supported beam structures shown in FIG.18 are maintained, applied forces and moments may be measured inaccordance with changes in the capacitance values of any particularcapacitive elements used in the force sensor 300 c, 301 c, 400 c, or 401c.

§ 5. Force Sensor According to a Fifth Embodiment of the PresentInvention

<5-1. Configuration of a Basic Structure>

Next, a force sensor according to a fifth embodiment of the presentinvention is described.

FIG. 29 is a schematic top view of a basic structure 500 of a forcesensor according to the fifth embodiment of the present invention. FIG.30 is a schematic side view of the basic structure 500 as viewed fromthe positive Y-axis side. This embodiment is described below, with theX-Y-Z three-dimensional coordinate system being defined as shown inFIGS. 29 and 30. For ease of explanation, a force receiving body 560 isnot shown in FIG. 29.

As shown in FIGS. 29 and 30, the basic structure 500 includes arectangular deformable body 510 that is a closed-loop rectangulardeformable body, and eight displacement bodies 520A through 520H. Therectangular deformable body 510 includes: four force receiving portions514A, 514B, 514D, and 514F; four fixed portions 515B, 515C, 515E, and515H arranged together with the four force receiving portions 514A,514B, 514D, and 514F alternately along a closed-loop path; and eightdeformable elements 510A through 510H that are disposed one by one inthe eight spaces formed between the force receiving portions and thefixed portions, which are adjacent to one another along the closed-looppath, and are elastically deformed by a force or a moment acting on theforce receiving portions 514A, 514B, 514D, and 514F. The displacementbodies 520A through 520H are connected to the deformable elements 510Athrough 510H, respectively, and are displaced by elastic deformationcaused in the deformable elements 510A through 510H.

As shown in FIG. 29, the four force receiving portions 514A, 514B, 514D,and 5114F are disposed on the positive X-axis, the negative X-axis, thepositive Y-axis, and the negative Y-axis, respectively, and are at equaldistances from the origin O. Meanwhile, the four fixed portions 515B,515C, 515E, and 515H are disposed one by one on a straight line thatpasses through the origin O and forms an angle of 45 degreescounterclockwise with respect to the positive X-axis, and on a straightline that passes through the origin O and forms an angle of 45 degreescounterclockwise with respect to the positive Y-axis, and are arrangedsymmetrically with respect to the origin O. These four fixed portions515B, 515C, 515E, and 515H form the four vertices of the rectangulardeformable body 510. Therefore, as shown in FIG. 29, the rectangulardeformable body 510 has a square shape when viewed from the Z-axisdirection.

As for the layout of the respective deformable elements 510A through510H of the rectangular deformable body 510, the first deformableelement 510A and the eighth deformable element 510H disposed on bothsides of the first force receiving portion 514A disposed on the negativeX-axis, and the fourth deformable element 510D and the fifth deformableelement 510E disposed on both sides of the third force receiving portion514D disposed on the positive X-axis both extend in parallel to theY-axis. Also, the second deformable element 510B and the thirddeformable element 510C disposed on both sides of the second forcereceiving portion 514B disposed on the positive Y-axis, and the sixthdeformable element 510F and the seventh deformable element 510G disposedon both sides of the fourth force receiving portion 514F disposed on thenegative Y-axis both extend parallel to the X-axis.

Next, the configuration of each of the deformable elements 510A through510H is described. In the description below, the configurations of thesecond and third deformable elements 510B and 510C are explained indetail with reference to FIGS. 29 and 30, and the configurations of theremaining deformation elements are described on the basis of theexplanation.

As shown in FIGS. 29 and 30, the second deformable element 510B that isdisposed parallel to the X-axis in the second quadrant (the upper leftregion in FIG. 29) of the X-Y plane is located between the first fixedportion 515B disposed on the negative X-axis side and the second forcereceiving portion 514B disposed on the Y-axis. The second deformableelement 510B includes a second tilting portion 513B having the Z-axisdirection (the depth direction in FIG. 29) as its longitudinaldirection, a 2-1st deformable portion 511B connecting the second forcereceiving portion 514B and the second tilting portion 513B, and a 2-2nddeformable portion 512B connecting the first fixed portion 515B and thesecond tilting portion 513B. As shown in FIG. 30, the 2-1st deformableportion 511B extends parallel to the X-Y plane, and is connected to thesecond tilting portion 513B at the end portion (the lower end portion inFIG. 30) of the second tilting portion 513B on the negative Z-axis side.The 2-2nd deformable portion 512B extends parallel to the X-Y plane, andis connected to the second tilting portion 513B at the end portion (theupper end portion in FIG. 30) of the second tilting portion 513B on thepositive Z-axis side.

As shown in FIGS. 29 and 30, the third deformable element 510C that isdisposed parallel to the X-axis in the first quadrant (the upper rightregion in FIG. 29) of the X-Y plane is located between the second fixedportion 515C disposed on the positive X-axis side and the second forcereceiving portion 514B disposed on the Y-axis. The third deformableelement 510C includes a third tilting portion 513C having the Z-axisdirection as its longitudinal direction, a 3-1st deformable portion 511Cconnecting the second force receiving portion 514B and the third tiltingportion 513C, and a 3-2nd deformable portion 5120 connecting the secondfixed portion 515C and the third tilting portion 513C. As shown in FIG.30, the 3-1st deformable portion 511C extends parallel to the X-Y plane,and is connected to the third tilting portion 513C at the end portion(the lower end) of the third tilting portion 5130 on the negative Z-axisside. The 3-2nd deformable portion 512C extends parallel to the X-Yplane, and is connected to the third tilting portion 513C at the endportion (the upper end) of the third tilting portion 513C on thepositive Z-axis side.

Further, although not specifically shown in the drawings, the firstdeformable element 510A and the eighth deformable element 510H disposedparallel to the Y-axis in the region where the X-coordinate is negative(the region on the left side of the Y-axis in FIG. 29) correspond to theconfigurations of the third deformable element 510C and the seconddeformable element 510B, respectively, if the second and thirddeformable elements 510B and 510C are rotated 90 degreescounterclockwise around the origin O.

Also, the fourth deformable element 510D and the fifth deformableelement 510E disposed parallel to the Y-axis in the region where theX-coordinate is positive (the region on the right side of the Y-axis inFIG. 29) correspond to the configurations of the second deformableelement 510B and the third deformable element 510C, respectively, if thesecond and third deformable elements 510B and 510C are rotated 90degrees clockwise around the origin O. The sixth deformable element 510Fand the seventh deformable element 510G disposed parallel to the X-axisin the region where the Y-coordinate is negative (the region on thelower side of the X-axis in FIG. 29) correspond to the configurations ofthe second deformable element 510B and the third deformable element510C, respectively, if the second and third deformable elements 5110Band 5110C, are rotated 180 degrees clockwise around the origin O.

As the above correspondence relationships have been described, the firstand fourth through eighth deformable elements 510A and 510D through 510Hare not described in detail herein. It should be noted that, in FIGS. 29and 30, “A” and “D” through “H” are attached to the ends of thereference numerals for the components of the first and fourth througheighth deformable elements 510A and 510D through 510H, respectively.

Further, the lower end portions of the respective fixed portions 515B,515C, 515E, and 515H of the basic structure 500 are connected to asupport 550, with a predetermined distance being kept from first througheighth beams 521A through 521H that will be described later.

As shown in FIGS. 29 and 30, the above described eight displacementbodies 520A through 520H are connected one by one to the lower ends (theend on the negative Z-axis side) of the respective tilting portions 513Athrough 513H of the first through eighth deformable elements 510Athrough 510H. Each of the displacement bodies 520A through 520H has adisplacement portion that is displaced by the tilting movement of thecorresponding one of the tilting portions 513A through 513H. As shown inFIGS. 29 and 30, the displacement portions are the first through eighthbeams 521A through 521H attached to the lower ends of the tiltingportions 513A through 513H via connecting bodies 522A through 522H,respectively.

The specific configuration of each of the displacement bodies 520Athrough 520H is the same as that of the first displacement body 220Adescribed in the second embodiment, Therefore, in FIGS. 29 and 30, thecomponents corresponding to those of the second embodiment are denotedby the same reference numerals as those used in the second embodiment,and detailed explanation thereof is not made herein. As will bedescribed later, capacitive elements are disposed in the displacementportions all through D82 of the respective displacement bodies 520Athrough 520H, so that forces and moments acting on the force receivingportions 514A, 514B, 514D, and 514F are detected. In short, the basicstructure 500 is formed with eight basic structures 100 as the firstthrough eighth deformable elements 510A through 510H arranged in arectangular closed-loop form, and each of the eight basic structures 100is the basic structure 100 described in § 1.

Further, as shown in FIG. 30, the force receiving body 560 (not shown inFIG. 29) for receiving the force to be detected is disposed on thepositive Z-axis side of the rectangular deformable body 510. The forcereceiving body 560 includes: a force receiving body main body 561 havinga rectangular shape that is exactly the same shape as the rectangulardeformable body 510 when viewed from the Z-axis direction; and forcereceiving portion connecting bodies 562 through 565 (563 through 565 arenot shown) provided on the portions of the force receiving body mainbody 561 facing the force receiving portions 514A, 514B, 514D, and 514Fof the rectangular deformable body 510. The force receiving portionconnecting bodies 562 through 565 are connected to the correspondingforce receiving portions 514A, 514B, 514D, and 514F, so that a force anda moment acting on the force receiving body main body 561 aretransmitted to the respective force receiving portions 514A, 514B, 514D,and 514F.

<5-2. Operation of the Basic Structure>

Next, operation of the above basic structure 500 is described.

(5-2-1. Where a Force +Fx is Applied)

FIG. 31 is a diagram for explaining displacements caused in therespective displacement bodies 520A through 520H of the basic structure500 in FIG. 29 when a force +Fx in the positive X-axis direction acts onthe force receiving body 560. The meanings of the symbols such as arrowsin the drawing are the same as those described in § 2.

When a force +Fx in the positive X-axis direction acts on the forcereceiving portions 514A, 514B, 514D, and 514F via the force receivingbody 560, the respective force receiving portions 514A, 514B, 514D, and514F are displaced in the positive X-axis direction. As a result, asshown in FIG. 31, the third deformable element 510C and the sixthdeformable element 510F are subjected to compressive force like thecompressive force shown in FIG. 3. In this case, the third tiltingportion 513C tilts counterclockwise, and the sixth tilting portion 513Ftilts clockwise. That is, the third beam 521C tilts counterclockwise,and the sixth beam 521F tilts clockwise. As a result, the 3-1stdisplacement portion D31 is displaced in the negative Z-axis direction,the 3-2nd displacement portion D32 is displaced in the positive Z-axisdirection, the 6-1st displacement portion D61 is displaced in thepositive Z-axis direction, and the 6-2nd displacement portion D62 isdisplaced in the negative Z-axis direction.

At the same time, as shown in FIG. 31, the second deformable element510B and the seventh deformable element 510G are subjected to tensileforce like the tensile force shown in FIG. 4. As a result, the secondtilting portion 513B tilts counterclockwise, and the seventh tiltingportion 513G tilts clockwise. That is, the second beam 521B tiltscounterclockwise, and the seventh beam 521G tilts clockwise. As aresult, the 2-1st displacement portion D21 is displaced in the negativeZ-axis direction, the 2-2nd displacement portion D22 is displaced in thepositive Z-axis direction, the 7-1st displacement portion D71 isdisplaced in the positive Z-axis direction, and the 7-2nd displacementportion D72 is displaced in the negative Z-axis direction.

Meanwhile, the two force receiving portions 514A and 514D positioned onthe X-axis move in a direction (the X-axis direction) orthogonal to thealignment direction (the Y-axis direction) of the first, fourth, fifth,and eighth deformable elements 510A, 510D, 510E, and 510H. Therefore, inthe capacitive elements C11, C12, C41, C42, C51, C52, C81, and C82corresponding to these four deformable elements 510A, 510D, 510E, and510H, some of the displacement electrodes Em11, Em12, Em41, Em42, Em51,Em52, Em81, and Em82, which form the respective capacitive elements, aredisplaced in the positive Z-axis direction, and the other ones of thedisplacement electrodes are displaced in the negative Z-axis direction.That is, the distance between electrode plates increases in some of thecapacitive elements, while the distance between electrode placesdecreases in the other capacitive elements. Therefore, it can beconsidered that none of the capacitance values of the eight capacitiveelements C11, C12, C41, C42, C51, C52, C81, and C82 substantiallychanges.

It should be noted that, when a force +Fy in the positive Y-axisdirection acts on the force receiving portions 514A, 514B, 514D, and514F of the basic structure 500, operation of the basic structure 500should be the same as the above described operation of the basicstructure 500 in the case where the force +Fx in the positive X-axisdirection is applied, except that all the aspects are rotated 90 degreescounterclockwise around the origin O. Therefore, detailed explanationthereof is not made herein.

(5-2-2. Where a Force +Fz is Applied)

FIG. 32 is a diagram for explaining displacements caused in therespective displacement bodies 520A through 520H of the basic structure500 in FIG. 29 when a force +Fz in the positive Z-axis direction acts onthe force receiving body 560. The meanings of the symbols such as arrowsin the drawing are the same as those described in § 2.

As the force +Fz in the positive Z-axis direction acts on the forcereceiving portions 514A, 514B, 514D, and 514F via the force receivingbody 560, the respective force receiving portions 514A, 514B, 514D, and514E are displaced in the positive Z-axis direction. As a result, asshown in FIG. 32, each of the first through eighth deformable elements510A through 510H is subjected to upward force like the upward forceshown in FIG. 6. In this case, the first, third, fifth, and seventhtilting portions 513A, 513C, 513E, and 513G tilt clockwise, and theremaining second, fourth, sixth, and eighth tilting portions 513B, 513D,513F, 513H tilt counterclockwise. That is, the first, third, fifth, andseventh beams 521A, 521C, 521E, and 521G tilt clockwise, and theremaining second, fourth, sixth, and eighth tilting portions 513B, 513D,513F, and 513H tilt counterclockwise.

As a result, the 1-1st, 2-2nd, 3-1st, 4-2nd, 5-1st, 6-2nd, 7-1st, and8-2nd displacement portions D11, D22, D31, D42, D51, D62, D71, and D82are displaced in the positive Z-axis direction, and the remaining 1-2nd,2-1st, 3-2nd, 4-1st, 5-2nd, 6-1st, 7-2nd, and 8-1st displacementportions D12, D21, D32, D41, D52, D61, D72, and D81 are displaced in thenegative Z-axis direction.

(5-2-3. Where a Moment +Mx is Applied)

Next, operation of the basic structure 500 when a moment +Mx around thepositive X-axis acts on the force receiving body 560 (force receivingportions) of the basic structure 500 is described.

FIG. 33 is a diagram for explaining displacements caused in therespective displacement bodies 520A through 520H of the basic structure500 in FIG. 29 when a moment +Mx around the positive X-axis acts on theforce receiving body 560. The meanings of the symbols such as arrows inthe drawing are the same as those described in § 2.

When the moment +Mx around the positive X-axis acts on the forcereceiving body 560, the second force receiving portion 514B located onthe positive Y-axis is displaced in the positive Z-axis direction(toward the front side in FIG. 33), and the fourth force receivingportion 514F located on the negative Y-axis is displaced in the negativeZ-axis direction (the depth direction in FIG. 33). Therefore, as shownin FIG. 33, the second and third deformable elements 510B and 510C aresubjected to upward force like the upward force shown in FIG. 6, as inthe case where the force +Fz is applied. That is, as described in5-2-2., the 2-1st and 3-2nd displacement portions D2.1 and D32 aredisplaced in the negative Z-axis direction, and the 2-2nd and 3-1stdisplacement portions D22 and D31 are displaced in the positive Z-axisdirection.

Meanwhile, as shown in FIG. 33, the sixth and seventh deformableelements 510F and 510G are subjected to downward force like the downwardforce shown in FIG. 5, which is the opposite of the force in the casewhere the force +Fz is applied. In this case, the sixth tilting portion513F tilts clockwise, and the seventh tilting portion 513G tiltscounterclockwise. That is, the sixth beam 52W tilts clockwise, and theseventh beam 521G tilts counterclockwise. As a result, the 6-1stdisplacement portion D61 and the 7-2nd displacement portion D72 aredisplaced in the positive Z-axis direction, and the 6-2nd displacementportion D62 and the 7-1st displacement portion D71 are displaced in thenegative Z-axis direction.

Meanwhile, the first and third force receiving portions 514A and 514Dlocated on the center axis line (on the X-axis) of the moment +Mx arenot substantially displaced. Therefore, neither compressive force nortensile force substantially acts on the first, fourth, fifth, and eighthdeformable elements 510A, 510D, 510E, and 510H connected to the firstand third force receiving portions 514A and 514D. That is, thedisplacement portions D11, D12, D41, D42, D51, D52, D81, and D82corresponding to the respective deformable elements 510A, 510D, 510E,and 510H are not displaced in the Z-axis direction by the moment Mxaround the X-axis.

It should be noted that, when a moment +My around the positive Y-axisacts on the force receiving portions 514A, 514B, 514D, and 514F of thebasic structure 500, operation of the basic structure 500 should be thesame as the above described operation of the basic structure 500 in thecase where the moment +Mx around the positive X-axis is applied, exceptthat all the aspects are rotated 90 degrees counterclockwise around theorigin O. Therefore, detailed explanation thereof is not made herein.

(5-2-4. Where a Moment +Mz is Applied)

FIG. 34 is a diagram for explaining displacements caused in therespective displacement bodies 520A through 520H of the basic structure500 in FIG. 29 when a moment +Mz around the positive Z-axis acts on theforce receiving body 560. The meanings of the symbols such as arrows inthe drawing are the same as those described in § 2.

When the moment +Mz around the positive Z-axis acts on the forcereceiving body 560, the first force receiving portion 514A located onthe negative X-axis is displaced in the negative X-axis direction, thesecond force receiving portion 514B located on the positive Y-axis isdisplaced in the negative X-axis direction, the third force receivingportion 514D located on the positive X-axis is displaced in the positiveY-axis direction, and the fourth force receiving portion 514F isdisplaced in the positive X-axis direction located on the negativeY-axis, as shown in FIG. 34. Therefore, as shown in FIG. 34, the second,fourth, sixth, and eighth deformable elements 510B, 510D, 510F, and 510Hare subjected to compressive force like the compressive force shown inFIG. 3. In this case, the second, fourth, sixth, and eighth tiltingportions 513B, 513D, 513F, and 513H tilt clockwise, and accordingly, thesecond, fourth, sixth, and eighth beams 521B, 521D, 521F, and 521H alsotilt clockwise. As a result, the 2-1st, 4-1st, 6-1st, and 8-1stdisplacement portions D21, D41, D61, and D81 are displaced in thepositive Z-axis direction, and the 2-2nd, 4-2nd, 6-2nd, and 8-2nddisplacement portions D22, D42, D62, and D82 are displaced in thenegative Z-axis direction,

Further, as shown in FIG. 34, the first, third, fifth, and seventhdeformable elements 510A, 510C, 510E, and 510G are subjected to tensileforce like the tensile force shown in FIG. 4. In this case, the first,third, fifth, and seventh tilting portions 513A, 513C, 513E, and 513Gtilt clockwise, and accordingly, the first, third, fifth, and seventhbeams 521A, 521C, 521E, and 521G also tilt clockwise. As a result, the1-1st, 3-1st, 5-1st, and 7-1st displacement portions D11, D31, D51, andD71 are displaced in the positive Z-axis direction, and the 1-2nd,3-2nd, 5-2nd, and 7-2nd displacement portions D12, D32, D52, and D72 aredisplaced in the negative Z-axis direction.

As a summary of the above description, FIG. 35 shows a list of thedirections of the tilting movements caused in the respective tiltingportions 513A through 513H of the basic structure 500 in FIG. 29 and thedisplacements caused in the respective displacement portions D11 throughD82 of the displacement bodies 520A through 520H in a case where theforces +Fx, +Fy, and +Fz, in the respective axis directions of the X-Y-Zthree-dimensional coordinate system, and the moments +Mx, +My, and +Mzaround the respective axes act on the force receiving body 560. In FIG.35, the directions of rotation (clockwise/counterclockwise) shown in thecolumns for the respective tilting portions 513A through 513H are thedirections observed from the origin O. Further, the symbol “+” writtenin the columns for the respective displacement portions all through D48means that the distance between the corresponding displacement portionand the support 550 increases, and the symbol “−” means that thedistance between the corresponding displacement portion and the support550 decreases.

In a case where the forces and moments acting on the force receivingbody 560 are in negative directions and in negative rotative directions,the directions of the tilting movements of the tilting portions 513Athrough 513H are all reversed from those in the above described cases.As a result, the directions of displacements caused in the displacementportions D11 through D82 of the respective displacement bodies 520Athrough 520H are also reversed, and the directions of the tiltingmovements and the increases/decreases (+/−) in the distance between therespective displacement portions D11 through D82 and the support 550 areall reversed from those shown in the list in FIG. 35.

<5-3. Structure of a Force Sensor>

Next, the structure of a force sensor 500 c including the basicstructure 500 described above in 5-1 and 5-2 is described.

FIG. 36 is a schematic top view of the force sensor 500 c according tothe fifth embodiment of the present invention using the basic structure500 shown in FIG. 29. FIG. 37 is a schematic side view of the forcesensor 500 c as viewed from the positive Y-axis side in FIG. 36.

As shown in FIGS. 36 and 37, the force sensor 500 c includes the abovedescribed basic structure 500 and a detection circuit 540 that detectsan applied force and an applied moment in accordance with displacementscaused in the respective displacement portions D11 through D82 of thedisplacement bodies 520A through 520H of the basic structure 500. Asshown in FIGS. 36 and 37, the detection circuit 540 of this embodimentincludes: sixteen capacitive elements C11 through C82 disposed one byone in the respective displacement portions D11 through D82 of thedisplacement bodies 520A through 520H; and a measuring unit 541 that isconnected to these capacitive elements C11 through C82, and measures theapplied force in accordance with changes in the capacitance values ofthe capacitive elements C11 through C82.

The specific configurations of the sixteen capacitive elements C11through C82 are as follows. Specifically, as shown in FIG. 37, the 2-1stcapacitive element C21 includes: a 2-1st displacement electrode Em21disposed on the 2-1st displacement portion D21 of the second beam 521Bvia an insulator (not shown); and a 2-1st fixed electrode Ef21 disposedon the support 550 via an insulator (not shown) in such a manner as toface the 2-1st displacement electrode Em21. Also, the 2-2nd capacitiveelement C22 includes: a 2-2nd displacement electrode Em22 disposed onthe 2-2nd displacement portion D22 of the second beam 521B via aninsulator (not shown); and a 2-2nd fixed electrode Ef22 disposed on thesupport 550 via an insulator (not shown) in such a manner as to face the2-2nd displacement electrode Em22.

Likewise, as shown in FIG. 37, the 3-1st capacitive element C31includes: a 3-1st displacement electrode Em31 disposed on the 3-1stdisplacement portion D31 of the third beam 221C via an insulator (notshown); and a 3-1st fixed electrode Ef31 disposed on the support 550 viaan insulator (not shown) in such a manner as to face the 3-1stdisplacement electrode Em31. The 3-2nd capacitive element C32 includes:a 3-2nd displacement electrode Em32 disposed on the 3-2nd displacementportion D32 of the third beam 521C via an insulator (not shown); and a3-2nd fixed electrode Ef32 disposed on the support 550 via an insulator(not shown) in such a manner as to face the 3-2nd displacement electrodeEm32.

Further, although not specifically shown in the drawings, the 1-1st,1-2nd, 8-1st, and 8-2nd capacitive elements C11, C12, C81, and C82disposed parallel to the Y-axis in the region where the X-coordinate isnegative (the region on the left side of the Y-axis in FIG. 36)correspond to the configurations of the capacitive elements C31, C32,C21, and C22, respectively, if the above described 3-1st, 3-2nd, 2-1st,and 2-2nd capacitive elements C31, C32, C21, and C22 are rotated 90degrees counterclockwise around the origin O.

Also, the 4-1st, 4-2nd, 5-1st, and 5-2nd capacitive elements C41, C42,C51, and C52 disposed parallel to the Y-axis in the region where theX-coordinate is positive (the region on the right side of the Y-axis inFIG. 36) correspond to the configurations of the capacitive elementsC31, C32, C21, and C22, respectively, if the above described 3-1st,3-2nd, 2-1st, and 2-2nd capacitive elements C31, C32, C21, and C22 arerotated 90 degrees clockwise around the origin O. The 6-1st, 6-2nd,7-1st, and 7-2nd capacitive elements disposed parallel to the X-axis inthe region where the Y-coordinate is negative (the region on the lowerside of the X-axis in FIG. 36) correspond to the configurations of thecapacitive elements C21, C22, C31, and C32, respectively, if the abovedescribed 2-1st, 2-2nd, 3-1st, and 3-2nd capacitive elements C21, C22,C31, and C32 are rotated 180 degrees clockwise around the origin O.

With the above described correspondence relationship, the capacitiveelements other than the 2-1st, 2-2nd, 3-1st, and 3-2nd capacitiveelements C21, C22, C31, and C32 are not specifically described herein.

Although not clearly shown in FIGS. 36 and 37, these capacitive elementsC11 through C82 are connected to the measuring unit 541 of the detectioncircuit 540 by a predetermined circuit, and the capacitance values ofthe capacitive elements C11 through C82 are supplied to the measuringunit 541.

<5-4. Operation of the Force Sensor>

Next, operation of the force sensor 500 c described in 5-3. isdescribed.

(5-4-1. Where a Force +Fx in the Positive X-Axis Direction is Applied)

When a force +Fx in the positive X-axis direction acts on the forcereceiving portions 514A, 514B, 514D, and 514F of the force sensor 500 cvia the force receiving body 560, the capacitance values of the 2-1st,3-1st, 6-2nd, and 7-2nd capacitive elements C21, C31, C62, and C72increase, while the capacitance values of the 2-2nd, 3-2nd, 6-1st, and7-1st capacitive elements C22, C32, C61, and C71 decrease, as can beseen from the displacements of the respective detection portions D11through D82 shown in FIG. 35. The capacitance values of the remaining1-1st, 1-2nd, 4-1st, 4-2nd, 5-1st, 5-2nd, 8-1st, and 8-2nd capacitiveelements C11, C12, C41, C42, C51, C52, C81, and C82 do not change.

FIG. 38 is a table as a list that shows the increases/decreases in thecapacitance values of the respective capacitive elements in a case wherethe forces +Fx, +Fy, and +Fz in the respective axis directions or themoments +Mx, +My, and +Mz around the respective axes in the X-Y-Zthree-dimensional coordinate system act on the force receiving portions514A, 514B, 514D, and 514F. The increases/decreases in the capacitancevalues of the above described capacitive elements C11 through C82 aresummarized in the column for Fx in FIG. 38. In the list, each symbol “+”indicates that the capacitance value increases, and each symbol “−”indicates that the capacitance value decreases.

In this embodiment, in the respective beams 521A through 521H, the firstdisplacement portions D11, D21, . . . , and D81, and the seconddisplacement portions D12, D22, . . . , and D82 are arranged at equaldistances from the centers of the tilting movements of the correspondingbeams 521A through 521H. Accordingly, in the four beams 521B, 521C,521F, and 521G in which tilting movement are caused, the magnitudes(|ΔC21|, |ΔC31|, |ΔC61|, and |ΔC71|) of the changes in the capacitancevalues of the capacitive elements C21, C31, C61, and C71 disposed in thefirst displacement portions D21, D31, D61, and D71 are equal to themagnitudes (|C22|, |ΔC32|, |ΔC62|, and |ΔC72|) of the changes in thecapacitance values of the capacitive elements C22, C32, C62, and C72disposed in the second displacement portions D22, D32, D62, and D72.Because of this, where|ΔC21|=|ΔC22|=|ΔC31|=|ΔC32|=|ΔC61|=|ΔC62|=|ΔC71|=|ΔC72|=|ΔC, therespective capacitance values C11 a through C82 a of the 1-1st through8-2nd capacitive elements C11 through C82 when the force is applied areexpressed by the following [Expression 21].C11a=C11C12a=C12C21a=C21+ΔCC22a=C22−ΔCC31a=C31+ΔCC32a=C32−ΔCC41a=C41C42a=C42C51a=C51C52a=C52C61a=C61−ΔCC62a=C62+ΔCC71a=C71−ΔCC72a=C72+ΔCC81a=C81C82a=C82  [Expression 21]

In accordance with such changes in the capacitance values, the measuringunit 541 measures the applied force +Fx by using the following[Expression 22].+Fx=C21−C22+C31−C32−C61+C62−C71+C72  [Expression 22]

(5-4-2. Where a Force +Fy in the Positive Y-Axis Direction is Applied)

When a force +Fy in the positive Y-axis direction acts on the forcereceiving portions 514A, 514B, 514D, and 514F of the force sensor 500 cvia the force receiving body 560, the capacitance values of the 1-1st,4-2nd, 5-2nd, and 8-1st capacitive elements C11, C42, C52, and C81increase, while the capacitance values of the 1-2nd, 4-1st, 5-1st, and8-2nd capacitive elements C12, C41, C51, and C82 decrease, as can beseen from the displacements of the respective detection portions D11through D82 shown in FIG. 35. The capacitance values of the remaining2-1st, 2-2nd, 3-1st, 3-2nd, 6-1st, 6-2nd, 7-1st, and 7-2nd capacitiveelements C21, C22, C31, C32, C61, C62, C71, and C72 do not change. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C82 are summarized in the column for Fy in FIG. 38.

In this case, in the respective beams 521A through 521H, the magnitudesof the changes in the capacitance values of the capacitive elements C11,C21, . . . , and C81 disposed in the first displacement portions D11,D21, . . . , and D81 can also be regarded as equal to the magnitudes ofthe changes in the capacitance values of the capacitive elements C12,C22, and C82 disposed in the second displacement portions D12, D22, andD82. Accordingly, taking into account the changes in the capacitancevalues of the respective capacitive elements C11 through C82 in the samemanner as in the above [Expression 21], the measuring unit 541 measuresthe applied force +Fy according to the following [Expression 23].+Fy=C11−C12−C41 +C42−C51+C52+C81−C82  [Expression 23]

(5-4-3. Where a Force +Fz in the Positive Z-Axis Direction is Applied)

When a force +Fz in the positive Z-axis direction acts on the forcereceiving portions 514A, 514B, 514D, and 514F of the force sensor 500 cvia the force receiving body 560, the capacitance values of the 1-2nd,2-1st, 3-2nd, 4-1st, 5-2nd, 6-1st, 7-2nd, and 8-1st capacitive elementsC12, C21, C32, C41, C52, C61, C72, and C81 increase, while thecapacitance values of the remaining 1-1st, 2-2nd, 3-1st, 4-2nd, 5-1st,6-2nd, 7-1st, and 8-2nd capacitive elements C11, C22, C31, C42, C51,C62, C71, and C82 decrease, as can be seen from the displacements of therespective detection portions D11 through D82 shown in FIG. 35. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C82 are summarized in the column for Fz in FIG. 38.

More specifically, when the force +Fz is applied, the respective tiltingportions 513A through 513H are displaced in the positive Z-axisdirection in total. Therefore, as described in detail in § 2, thedisplacements caused in the respective displacement portions D11 throughD82 are the sums of the displacements in the positive Z-axis directionor the negative Z-axis direction due to the tilting movements of therespective tilting portions 513A through 513K and the displacements ofthe respective tilting portions 513A through 513H in the positive Z-axisdirection. That is, in the displacement portions D11, D22, D31, D42,D51, D62, D71, and D82 that are displaced in the positive Z-axisdirection, the displacements are amplified. In the displacement portionsD12, D21, D32, D41, D52, D61, D72, and D81 that are displaced in thenegative Z-axis direction, the displacements are offset.

Here, the length of the respective beams 521A through 521H in the Z-axisdirection is sufficiently greater than the length (height) of therespective tilting portions 513A through 521H in the Z-axis direction.In view of this, the magnitudes (|ΔC11|, |ΔC21|, . . . , and |ΔC81|) ofthe changes in the capacitance values of the capacitive elements C11,C21, . . . , and C81 provided in the first displacement portions D11,D21, . . . , and D81 of the respective beams 521A through 521H can beregarded as equal to the magnitudes (|ΔC12|, |ΔC22|, . . . , and |ΔC82|)of the changes in the capacitance values of the capacitive elements C12,C22, . . . , and C82 provided in the second displacement portions D12,D22, . . . , and D82.

Accordingly, taking into account the changes in the capacitance valuesof the respective capacitive elements C11 through C82 in the same manneras in the above [Expression 21], the measuring unit 541 measures theapplied force +Fz according to the following [Expression 24].+Fz=−C11+C12+C21−C22−C31+C32+C41−C42−C51+C52+C61−C62−C71+C72+C81−C82  [Expression24]

(5-4-4. Where a Moment +Mx Around the Positive X-Axis is Applied)

When a moment +Mx around the positive X-axis acts on the force receivingportions 514A, 514B, 514D, and 514F of the force sensor 500 c via theforce receiving body 560, the capacitance values of the 2-1st, 3-2nd,6-2nd, and 7-1st capacitive elements C21, C32, C62, and C71 increase,while the capacitance values of the 2-2nd, 3-1st, 6-1st, and 7-2ndcapacitive elements C22, C31, C61, and C72 decrease, as can be seen fromthe displacements of the respective detection portions D11 through D82shown in FIG. 35. The capacitance values of the remaining 1-1st, 1-2nd,4-1st, 4-2nd, 5-1st, 5-2nd, 8-1st, and 8-2nd capacitive elements C11,C12, C41, C42, C51, C52, C81, and C82 do not change. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C82 are summarized in the column for Mx in FIG. 38.

In this case, in the respective beams 521A through 521H, the magnitudesof the changes in the capacitance values of the capacitive elements C11,C21, . . . , and C81 disposed in the first displacement portions D11,D21, . . . , and D81 can also be regarded as equal to the magnitudes ofthe changes in the capacitance values of the capacitive elements C12,C22, . . . , and C82 disposed in the second displacement portions D12,D22, and D82. Accordingly, taking into account the changes in thecapacitance values of the respective capacitive elements C11 through C82in the same manner as in the above [Expression 21], the measuring unit541 measures the applied moment +Mx according to the following[Expression 25].+Mx=C21−C22−C31+C32−C61+C62+C71−C72  [Expression 25]

(5-4-5. Where a Moment +My Around the Positive Y-Axis is Applied)

When a moment +My around the positive Y-axis acts on the force receivingportions 514A, 514B, 514D, and 514F of the force sensor 500 c via theforce receiving body 560, the capacitance values of the 1-2nd, 4-2nd,5-1st, and 8-1st capacitive elements C12, C42, C51, and C81 increase,while the capacitance values of the 1-1st, 4-1st, 5-2nd, and 8-2ndcapacitive elements C11, C41, C52, and C82 decrease, as can be seen fromthe displacements of the respective detection portions D11 through D82shown in FIG. 35. The capacitance values of the remaining 2-1st, 2-2nd,3-1st, 3-2nd, 6-1st, 6-2nd, 7-1st, and 7-2nd capacitive elements C21,C22, C31, C32, C61, C62, C71, and C72 do not change. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C82 are summarized in the column for My in FIG. 38.

In this case, in the respective beams 521A through 521H, the magnitudesof the changes in the capacitance values of the capacitive elements C11,C21, . . . , and C81 disposed in the first displacement portions D11,D21, . . . , and D81 can also be regarded as equal to the magnitudes ofthe changes in the capacitance values of the capacitive elements C12,C22, and C82 disposed in the second displacement portions D12, D22, . .. , and D82. Accordingly, taking into account the changes in thecapacitance values of the respective capacitive elements C11 through C82in the same manner as in the above [Expression 21], the measuring unit541 measures the applied moment +My according to the following[Expression 26].+My=−C11+C12−C41+C42+C51−C52+C81−C82  [Expression 26]

(5-4-6. Where a Moment +Mz Around the Positive Z-Axis is Applied)

When a moment +Mz around the positive Z-axis acts on the force receivingportions 514A, 514B, 514D, and 514F of the force sensor 500 c via theforce receiving body 560, the capacitance values of the 1-2nd, 2-2nd,3-2nd, 4-2nd, 5-2nd, 6-2nd, 7-2nd, and 8-2nd capacitive elements C12,C22, C32, C42, C52, C62, C72, and C82 increase, while the capacitancevalues of the remaining 1-1st, 2-1st, 3-1st, 4-1st, 5-1st, 6-1st, 7-1st,and 8-1st capacitive elements C11, C21, C31, C41, C51, C61, C71, and C81decrease, as can be seen from the displacements of the respectivedetection portions D11 through D82 shown in FIG. 35. Theincreases/decreases in the capacitance values of these capacitiveelements C11 through C82 are summarized in the column for Mz in FIG. 38.

In this case, in the respective beams 521A through 521H, the magnitudesof the changes in the capacitance values of the capacitive elements C11,C21, and C81 disposed in the first displacement portions D11, D21, . . ., and D81 can also be regarded as equal to the magnitudes of the changesin the capacitance values of the capacitive elements C12, C22, and C82disposed in the second displacement portions D12, D22, . . . , and D82.Accordingly, taking into account the changes in the capacitance valuesof the respective capacitive elements C11 through C82 in the same manneras in the above [Expression 21], the measuring unit 541 measures theapplied moment +Mz according to the following [Expression 27].+Mz=−C11+C12−C21+C22−C31+C32−C41+C42−C51+C52−C61+C62−C71+C72−C81+C82  [Expression27]

It should be noted that, in cases where the negative forces −Fx, −Fy,and −Fz in the respective axis directions or the moments −Mx, −My, and−Mz around the respective negative axes act on the force receiving body560 of the force sensor 500 c, the increases/decreases in the distancesbetween the electrodes of the respective capacitive elements C11 throughC82 are reversed from those shown in FIG. 35, as described above.Therefore, to detect the forces −Fx, −Fy, and −Fz or the moments −Mx,−My, and −Mz, the signs of C11 through C82 in the right sides of[Expression 22] through [Expression 27] should be reversed.

<5-5. Other-Axis Sensitivity of the Force Sensor>

Referring now to FIG. 39, the other-axis sensitivity of the force sensor500 c according to this embodiment is described. FIG. 39 is a table as alist that shows the other-axis sensitivities VFx through VMz of theforces Fx, Fy, and Fz in the respective axis directions and the momentsMx, My, and Mz around the respective axes in the force sensor 500 cshown in FIG. 36, The numbers shown in the table in FIG. 39 are valuesobtained by assigning the respective forces Fx, Fy, and Fz, and therespective moments Mx, My, and Mz in the table shown in FIG. 38 to therespective right sides of the above [Expression 22] through [Expression27]. Each capacitive element with the symbol “+” is represented by +1,and each capacitive element with the symbol “−” is represented by −1, asdescribed in 2-5.

As can be seen from FIG. 39, the other-axis sensitivities of the forcesFx, Fy, and Fz in the respective axis directions and the moments Mx, My,and Mz around the respective axes are zero. Accordingly, the forcesensor 500 c shown in FIG. 36 can detect all the forces Fx, Fy, and Fzin the respective axis directions, and the moments Mx, My, and Mz aroundthe respective axes.

In the actual force sensor 500 c, however, there is a slight change inthe capacitance value even in a capacitive element that has a “0” changein its capacitance value in FIG. 38. Further, in a case where the forceFz and the moments Mx and My act on the force receiving body 560,displacements in the Z-axis direction are caused in the tilting portions513A through 513H, as described above. Therefore, the magnitudes of theZ-axis direction displacements caused in the first displacement portionsD11, D21, and D81 differ from the magnitudes of the Z-axis directiondisplacements caused in the second displacement portions D21, D22, andD82. As is apparent from these facts, there is a slight other-axissensitivity in practice. However, even in such a case, the other-axissensitivity can be reduced to zero through a correcting operation inwhich an inverse matrix of an actual matrix of other-axis sensitivities(a matrix of six rows and six columns corresponding to the table shownin FIG. 39) is calculated, and the output of the force sensor 500 c ismultiplied by this inverse matrix.

According to this embodiment described above, displacements caused inthe tilting portions 513A through 513H can be easily amplified by theactions of the beams 521A through 521H that are displaced by the tiltingmovements of the tilting portions 513A through 513H. Further, with theuse of the 1-1st through 8-2nd capacitive elements C11 through C82, allof the applied forces Fx, Fy, and Fz and applied moments Mx, My, and Mzcan be detected in accordance with differences between changes in thecapacitance values of these capacitive elements. That is, thisembodiment can provide the force sensor 500 c that is inexpensive buthighly sensitive, and is hardly affected by temperature changes orin-phase noise in the use environment.

Further, the displacement bodies 520A through 520H include connectingbodies 522A through 522H connecting the corresponding tilting portions513A through 513H and the beams 521A through 521B, respectively, and thefirst displacement portions D11, D21, . . . , and D81 and the seconddisplacement portions D12, D22, . . . , and D82 of the displacementbodies 520A through 520H are arranged symmetrically with respect to theconnecting portions between the connecting bodies 522A through 522H andthe corresponding beams 521A through 521H. Because of this, thedisplacements caused in the first displacement portions D11, D21, . . ., and D81 and the displacements caused in the second displacementportions D12, D22, and D82 are of the same magnitude but have differentsigns from each other. Thus, applied forces and moments can be detectedthrough simple calculations.

The force sensor 500 c also includes: the force receiving body 560 thatis connected to the force receiving portions 514A, 514B, 514D, and 514Fof the deformable body 510, and receives the applied forces Fx, Fy, andFz and the moments Mx, My, and Mz; and the support 550 that is disposedto face the displacement bodies 520A through 520H, and is connected tothe four fixed portions 515B, 515C, 515E, and 515H of the deformablebody 510. With this arrangement, it is possible to transmit the appliedforces Fx, Fy, and Fz and the moments Mx, My, and Mz to the deformablebody 510 without fail.

Further, the deformable body 510 has a square shape. The four forcereceiving portions 514A, 514B, 514D, and 514F are positioned at themidpoints of the respective sides of the square, and the four fixedportions 515B, 515C, 515E, and 515H are positioned at the respectivevertices. With this arrangement, calculations for detecting the appliedforces Fx, Fy, and Fz, and the moments Mx, My, and Mz are easy.

§ 6. Force Sensor According to a Sixth Embodiment of the PresentInvention

<6-1. Configuration of a Basic Structure>

The force sensor 500 c described in § 5 is capable of detecting the sixcomponents of the forces Fx, Fy, and Fz and moments Mx, My, and Mz inthe respective axis directions. However, to detect these six components,it is not always necessary to provide sixteen capacitive elements in aforce sensor.

In the description below, a force sensor capable of detecting the sixcomponents with fewer capacitive elements according to a sixthembodiment will be described as a modification of the above describedforce sensor 500 c.

FIG. 40 is a schematic top view of a force sensor 600 c according to thesixth embodiment of the present invention. FIG. 41 is a schematic sideview of the force sensor 600 c as viewed from the positive Y-axis side.

As shown in FIG. 40, the force sensor 600 c differs from the forcesensor 500 c according to the fifth embodiment in that all beams 621Athrough 621H are designed as cantilever beams. Specifically, in thesecond, third, sixth, and seventh beams 621B, 621C, 621F, and 621Gextending in parallel to the X-axis, the top end portions in thecounterclockwise direction in FIG. 40 are removed, with respectiveconnecting bodies 622B, 622C, 622F, and 622G in the middle being left.On the other hand, in the first, fourth, fifth, and eighth beams 621A,621D, 621E, and 621H extending in parallel to the Y-axis, the top endportions in the clockwise direction in FIG. 40 are removed, withrespective connecting bodies 622A, 622D, 622E, and 622H in the middlebeing left.

Therefore, in the force sensor 600 c, a total of eight displacementportions D11, D22, D32, D41, D51, D62, D72, and D81 are formed one byone in the respective beams 621A through 621H. A total of eightcapacitive elements C11, C22, C32, C41, C51, C62, C72, and C81 aredisposed one by one at these eight displacement portions. Theconfiguration of each of the capacitive elements is the same as that ofthe fifth embodiment.

Although not shown in FIGS. 40 and 41, the eight capacitive elements areconnected to a measuring unit 641 of a detection circuit 640 by apredetermined circuit, and the capacitance values of the respectivecapacitive elements are supplied to the measuring unit 641. As describedlater, the measuring unit 641 detects forces and moments acting on theforce sensor 600 c, in accordance with changes in the capacitance valuesof the respective capacitive elements.

The other aspects of the force sensor 600 c are the same as those of thefifth embodiment. Therefore, the same components as those of the fifthembodiment are denoted by substantially the same reference numerals asthose used in the fifth embodiment, and detailed explanation thereof isnot made herein,

Next, operation of the force sensor 600 c according to this embodimentis described. The following is a description of a case where all the sixcomponents of forces Fx, Fy, and Fz in the respective axis directionsand moments Mx, My, and Mz around the respective axes in the X-Y-Zthree-dimensional coordinate system are detected.

As described above, the force sensor 600 c according to this embodimenthas substantially the same structure as the force sensor 500 c accordingto the fifth embodiment, except that the beams 621A through 621H aredesigned as cantilever beams. Accordingly, when a force or a moment actson force receiving portions 614A, 614B, 614D, and 614F via a forcereceiving body 660, the detection portions D11, D22, D32, D41, D51, D62,D72, and D81 of the respective beams 621A through 621H have the samedisplacements as those of the corresponding detection portions D11, D22,D32, D41, D51, D62, D72, and D81 of the force sensor 500 c according tothe fifth embodiment.

Because of the above, when the six components Fx, Fy, Fz, Mx, My, and Mzof forces and moments act on the force sensor 600 c, the capacitancevalues of the respective capacitive elements change as shown in a listin FIG. 42. In the list, each symbol “+” indicates that the capacitancevalue increases, and each symbol “−” indicates that the capacitancevalue decreases, as in FIG. 38. It should be noted that, in the table inFIG. 42, the increases/decreases in the capacitance values of the eightcapacitive elements C11, C22, C32, C41, C51, C62, C72, and C81 areidentical to those shown in FIG. 38.

In accordance with such changes in the capacitance values, the measuringunit 641 measures the applied forces and moments according to[Expression 28] shown below. [Expression 28] is the same as theexpression formed by deleting C12, C21, C31, C42, C52, C61, C71, and C82from the respective expressions of [Expression 22] through [Expression27].+Fx=−C22−C32+C62+C72+Fy=C11−C41−C51+C81+Fz=−C11−C22+C32+C41−C51−C62+C72+C81+Mx=−C22+C32+C62−C72+My=−C11−C41+C51+C81+Mz=−C11+C22+C32−C41−C51+C62+C72−C81  [Expression 28]

Where the other-axis sensitivities of the six components of forces andmoments are calculated according to [Expression 28], the results are asshown in a list in FIG. 43. The other-axis sensitivities are valuesobtained by assigning the force Fz and the moments Mx, My, and Mz in thetable shown in FIG. 23 to the right sides of the respective expressionsin the above [Expression 28]. Each capacitive element with the symbol“+” is represented by +1, and each capacitive element with the symbol“−” is represented by −1, as in FIG. 21. As shown in FIG. 43, theother-axis sensitivity of each component is zero. Furthermore, as can beseen from [Expression 28], each component is detected from differencesbetween the electrostatic capacitance values in this embodiment.Accordingly, the detection results are hardly affected by temperaturechanges or in-phase noise in the surrounding environment.

According to this embodiment described above, it is possible to providethe force sensor 600 c that can achieve the same effects as those of theforce sensor 500 c according to the fifth embodiment.

§ 7. Force Sensor According to a Seventh Embodiment of the PresentInvention and Modifications Thereof 7-1. Force Sensor According to aSeventh Embodiment

Next, a force sensor according to a seventh embodiment of the presentinvention is described.

FIG. 44 is a schematic top view of a force sensor 700 c according to theseventh embodiment of the present invention. This embodiment is alsodescribed below, with the X-Y-Z three-dimensional coordinate systembeing defined as shown in FIG. 44. For ease of explanation, a forcereceiving body 760 is not shown in FIG. 44.

As shown in FIG. 44, the force sensor 700 c differs from the fifthembodiment in that the rectangular deformable body 510 of the fifthembodiment is rounded at its four corners, and is designed as an annulardeformable body 710 with the origin O at its center. For example, thelongitudinal direction of the first beam 521A of the force sensor 500 caccording to the fifth embodiment is parallel to the Y-axis. However,the longitudinal direction of a first beam 721A of this embodiment isnot parallel to the Y-axis. Specifically, the first beam 721A isdisposed so as to be orthogonal to the straight line connecting theorigin O and a first connecting body 722A. Such positioning is the sameas the positioning of second through eighth beams 721B through 721H.

Next, operation of the above force sensor 700 c is described.

In the force sensor 700 c, the layout of respective deformable elements710A through 710H is roughly the same as that of the fifth embodiment.Therefore, when a force −Fx in the positive X-axis direction acts on theforce sensor 700 c, for example, the 2-1st, 3-1st, 6-2nd, and 7-2nddisplacement portions D21, D31, D62, and D72 are displaced in thenegative Z-axis direction, and the 2-2nd, 3-2nd, 6-1st, and 7-1stdisplacement portions D22, D32, D61, and D71 are displaced in thepositive Z-axis direction, as shown in FIG. 35.

Further, in this embodiment, the longitudinal directions of the beams721A through 721H are not parallel to the X-axis and the Y-axis, asdescribed above. Therefore, Z-axis direction displacements of relativelysmall values are also caused in the 1-1st, 1-2nd, 4-1st, 4-2nd, 5-1st,5-2nd, 8-1st, and 8-2nd displacement portions D11, D12, D41, D42, D51,D52, D81, and D82, which are not displaced in the Z-axis direction inthe fifth embodiment, Specifically, it is considered that the first,fourth, fifth, and eighth deformable elements 710A, 710D, 710E, and710H; correspond to the first through fourth deformable elements 210Athrough 210D, respectively, of the basic structure 200 (see FIG. 8)described in § 2. Therefore, the 1-1st, 4-1st, 5-2nd, and 8-2nddisplacement portions D11, D41, D52, and D82 are displaced in thenegative Z-axis direction, and the 1-2nd, 4-2nd, 5-1st, and 8-1stdisplacement portions D12, D42, D51, and D81 are displaced in thepositive Z-axis direction. This also applies in a where a force +Fy inthe positive Y-axis direction is applied.

In a case where a force +Fz in the positive Z-axis direction and moments+Mx, +My, and +Mz around the respective positive axes are applied, onthe other hand, the changes in the distances between the electrodes ofthe respective capacitive elements C11 through C82 are the same as thoseof the fifth embodiment.

FIG. 45 is a table as a list showing the directions of the tiltingmovements of the respective tilting portions 713A through 713H of theforce sensor in FIG. 44, and the displacements caused in the respectivedisplacement portions D11 through D82 in a case where forces in therespective axis directions and moments Fx through Mz in the respectiveaxis directions in the X-Y-Z three-dimensional coordinate system act onforce receiving portions.

In the table shown in FIG. 45, the signs of tilting movement directionsand displacements are shown in parentheses in the columns correspondingto the tilting portions that exhibit relatively small tilt movements andthe displacement portions that exhibit relatively small displacementswhen the deformable elements exhibit relatively small elasticdeformations. It should be noted that the table shown in FIG. 45 is thesame as that shown in FIG. 35, except for the columns showingparentheses. Although not shown, the signs of the displacements writtenin the columns for the displacement portions D11 through D82corresponding to the capacitive elements C11 through C82 in the table inFIG. 45 should be reversed, to obtain the changes caused in thecapacitance values of the respective capacitive elements C11 through C82in a case where forces in the respective axis directions and moments inthe respective axis directions Fx through Mz in the X-Y-Zthree-dimensional coordinate system are applied. It should be understoodthat each sign “+” indicates an increase in capacitance value, and eachsign “−” indicates a decrease in capacitance value.

A measuring unit 741 measures the applied forces and moments Fx throughMz according to [Expression 29] shown below.+Fx=C11−C12+C21−C22+C31−C32+C41−C42−C51+C52−C61+C62−C71+C72−C81+C82+Fy=C11−C12+C21−C22−C31+C32−C41+C42−C51+C52−C61+C62+C71−C72+C81−C82+Fz=−C11+C12+C21−C22−C31+C32+C41−C42−C51+C52+C61−C62−C71+C72+C81−C82+Mx=C21−C22−C31+C32−C61+C62+C71−C72+My=−C11+C12−C41+C42+C51−C52+C81−C82+Mz=−C11+C12−C21+C22−C31+C32−C41+C42−C51+C52−C61+C62−C71+C72−C81+C82  [Expression29]

It should be noted that, in cases where forces −Fx, −Fy, and −Fz in thenegative axis directions or moments −Mx, −My, and −Mz around thenegative axes act on the force receiving body 760 of the force sensor700 c, the Z-axis direction displacements of the respective displacementportions D11 through D82 are reversed from those shown in FIG. 45, asdescribed above. Therefore, to detect the forces −Fx, −Fy, and −Fz, orthe moments −Mx, −My, and −Mz, the signs of C11 through C82 in the rightsides of [Expression 29] should be reversed.

In the force sensor 700 c according to this embodiment, changes arecaused even in the capacitance values of the capacitive elements thathave no changes in the capacitance values in the fifth embodiment, asdescribed above.

Because of this, there exist other-axis sensitivities in thisembodiment. However, the other-axis sensitivities can be reduced to zerothrough a correcting operation in which an inverse matrix of an actualmatrix of other-axis sensitivities is calculated, and the output of theforce sensor 700 c is multiplied by this inverse matrix, as describedabove.

According to this embodiment described above, it is possible to providethe force sensor 700 c that can achieve the same effects as those of theforce sensor 500 c according to the fifth embodiment.

7-2. Modification

The force sensor 700 c described in 7-1 is capable of detecting the sixcomponents of the forces Fx, Fy, and Fz and moments Mx, My, and Mz inthe respective axis directions. However, to detect these six components,it is not always necessary to provide sixteen capacitive elements in aforce sensor. In the description below, a force sensor 701 c capable ofdetecting the six components with fewer capacitive elements will bedescribed as a modification of the above described force sensor 700 c.

FIG. 46 is a schematic top view of the force sensor 701 c according to amodification of FIG. 44.

As shown in FIG. 46, the force sensor 701 c differs from the forcesensor 700 c according to the seventh embodiment in that the beams 721Athrough 721H are designed as cantilever beams. Specifically, in thesecond, third, sixth, and seventh beams 721B, 721C, 721F, and 721G, thetop end portions in the counterclockwise direction in FIG. 46 areremoved, with respective connecting bodies 722B, 722C, 722F, and 722G inthe middle being left. On the other hand, in the first, fourth, fifth,and eighth beams 721A, 721D, 721E, and 721H, the top end portions in theclockwise direction in FIG. 46 are removed, with respective connectingbodies 722A, 722D, 722E, and 722H in the middle being left.

Therefore, in the force sensor 701 c, a total of eight displacementpotions D11, D22, D32, D41, D51, D62, D72, and D81 are formed one by onein the respective beams 721A through 721H. A total of eight capacitiveelements C11, C22, C32, C41, C51, C62, C72, and C81 are disposed one byone at these eight displacement portions. The configuration of each ofthe capacitive elements is the same as that of the fifth through seventhembodiments.

Although not shown in FIG. 46, the eight capacitive elements areconnected to the measuring unit 741 of a detection circuit 740 by apredetermined circuit, and the capacitance values of the respectivecapacitive elements are supplied to the measuring unit 741. As describedlater, the measuring unit 741 detects forces and moments acting on theforce sensor 701 c, in accordance with changes in the capacitance valuesof the respective capacitive elements.

The other aspects of the force sensor 701 c are the same as those of theseventh embodiment. Therefore, the same components as those of theseventh embodiment are denoted by the same reference numerals as thoseused in the seventh embodiment, and detailed explanation thereof is notmade herein. In short, the force sensor 700 c according to the seventhembodiment is the same as the force sensor 500 c according to the fifthembodiment, except that the deformable shape is changed to an annularshape. The force sensor 701 c according to this modification is the sameas the force sensor 600 c according to the sixth embodiment, except thatthe shape of the deformable body is changed into an annular shape.

Next, the operation of the force sensor 701 c according to thisembodiment is described. The following is a description of a case whereall the six components of forces Fx, Fy, and Fz in the respective axisdirections and moments Mx, My, and Mz around the respective axes in theX-Y-Z three-dimensional coordinate system are detected.

As described above, the force sensor 701 c according to thismodification has substantially the same structure as the force sensor700 c according to the seventh embodiment, except that the beams 721Athrough 721H are designed as cantilever beams. Accordingly, when a forceor a moment acts on the force receiving portions 714A, 714B, 714D, and714F via the force receiving body 760, the detection portions D11, D22,D32, D41, D51, D62, D72, and D81 of the respective beams 721A through721H have the same displacements as those of the corresponding detectionportions D11, D22, D32, D41, D51, D62, D72, and D81 of the force sensor700 c according to the seventh embodiment.

In view of the above, in a case where the six components Fx, Fy, Fz, Mx,My, and Mz of forces and moments act on the force sensor 701 c, theincreases/decreases in the capacitance values of respective capacitiveelements are identical to the increases/decreases in the capacitancevalues of the corresponding eight capacitive elements C11, C22, C32,C41, C51, C62, C72, and C81 in a case where the forces and the momentsact on the force sensor 700 c according to the seventh embodiment.

In accordance with such changes in the capacitance values, the measuringunit 741 measures the applied forces and moments according to[Expression 30] shown below. [Expression 30] is the same as theexpression formed by deleting C12, C21, C31, C42, C52, C61, C71, and C82from the respective expressions in [Expression 29].+Fx=C11−C22−C32+C41−C51+C62+C72−C81+Fy=C11−C22+C32−C41−C51+C62−C72+C81+Fz=−C11−C22+C32+C41−C51−C62+C72−C82+Mx=−C22+C32+C62−C72+My=−C11−C41+C51+C81+Mz=−C11+C22+C32−C41−C51+C62+C72−C81  [Expression 30]

It should be noted that, in cases where negative forces −Fx, −Fy, and−Fz in the respective axis directions or moments −Mx, −My, and −Mzaround the respective negative axes act on the force receiving body 760of the force sensor 701 c, the increases/decreases in the distancesbetween the electrodes of the respective capacitive elements arereversed from those shown in FIG. 45 with respect to the correspondingdisplacement portions, as described above. Therefore, to detect theforces −Fx, −Fy, and −Fz or the moments −Mx, −My, and −Mz, the signs ofC11 through C81 in the right sides of [Expression 30] should bereversed.

In the force sensor 701 c according to this modification, other-axissensitivities can also be reduced to zero through the above describedcorrecting operation.

According to this modification described above, it is possible toprovide the force sensor 701 c that can achieve the same effects asthose of the force sensor 700 c according to the seventh embodiment.

§ 8. Force Sensor According to an Eighth Embodiment of the PresentInvention

<8-1. Structure of a Force Sensor>

Next, a force sensor 800 c according to an eighth embodiment of thepresent invention is described.

FIG. 47 is a schematic top view of the basic structure 800 of a forcesensor 800 c according to the eighth embodiment of the presentinvention. FIG. 48 is a schematic top view of the basic structure 800.

As shown in FIGS. 47 and 48, the overall structure of the basicstructure 800 is the same as that of the first embodiment described in§ 1. Further, the capacitive elements C1 and C2 provided in the basicstructure 800 are also the same as those of the first embodiment (seeFIG. 7). Therefore, in FIGS. 47 and 48, the same components as those ofthe basic structure 100 according to the first embodiment are denoted bysubstantially the same reference numerals as those used in the firstembodiment, and detailed explanation thereof is not made herein. In thisembodiment, however, the length of a connecting body 822 in the Z-axisdirection, and the distance from the longitudinal direction 1 of atilting portion 813 to a second displacement portion D2 are set so thatthe second displacement portion D2 is not displaced in the Z-axisdirection when a force −Fz in the negative Z-axis direction acts on aforce receiving portion 814. This aspect will be described below indetail.

FIG. 49 is a schematic front view of the basic structure 800 in adeformed state when a force −Fx in the negative X-axis direction acts onthe force receiving portion 814. As described in § 1, when a force −Fzin the negative Z-axis direction acts on the force receiving portion814, a force in the negative Z-axis direction (the downward direction inFIG. 47) acts on a connecting portion R1 at the lower left end of thetilting portion 813, and a force in the positive Z-axis direction (theupward direction in FIG. 47) acts as a reaction of the applied force −Fzon a connecting portion R2 at the upper right end of the tilting portion813.

Because of the actions of these forces, the tilting portion 813 tiltscounterclockwise as shown in FIG. 49. Furthermore, because of the actionof the applied force −Fz, the tilting portion 813 is pulled downward inthe negative Z-axis direction via a first deformable portion 811, andaccordingly, the entire tilting portion 813 is slightly displaced in thenegative Z-axis direction.

At the same time, due to the tilting movement of the tilting portion813, a beam 821 connected to the lower end of the tilting portion 813also tilts counterclockwise as shown in FIG. 49. As a result, the firstdisplacement portion D1 of the beam 821 is displaced in the direction(the downward direction in FIG. 49) in which the distance to a support850 decreases, and the second displacement portion D2 is displaced inthe direction (the upward direction in FIG. 49) in which the distance tothe support 850 increases. More specifically, the displacement caused inthe first displacement portion D1 when the force −Fz is applied is thesum of the overall displacement of the above described tilting portion813 in the negative Z-axis direction and the displacement in thenegative Z-axis direction due to the tilting movement of the beam 821,and the displacement caused in the second displacement portion D2 is thesum of the overall displacement of the tilting portion 813 in thenegative Z-axis direction and the displacement in the positive Z-axisdirection due to the tilting movement of the beam 821. That is, when theforce −Fz in the negative Z-axis direction acts on the force receivingportion 814, the overall displacement of the tilting portion 813 in thenegative Z-axis direction is added to the displacement due to thetilting movement of the beam 821 in the first displacement portion D1.Therefore, the distance between the first displacement portion D1 andthe support 850 greatly decreases. In the second displacement portionD2, on the other hand, the displacement due to the tilting movement ofthe beam 821 is offset by the overall displacement of the tiltingportion 813 in the negative Z-axis direction. Therefore, the change inthe distance between a second displacement electrode Em2 and a secondfixed electrode Ef2 remains small. Particularly, in a case where thelength of the connecting body 822 in the Z-axis direction and thedistance from the longitudinal direction 1 of the tilting portion 813 tothe second displacement portion D2 are in a predetermined relationship,it is possible to maintain substantially a constant distance between thesecond displacement electrode Em2 and the second fixed electrode Ef2.This fact was taken into consideration in devising this embodiment.

Specifically, in a case where the length of the connecting body 822 inthe Z-axis direction and the distance from the longitudinal direction 1of the tilting portion 813 to the second displacement portion D2 are inthe predetermined relationship, the capacitance values C1 a and C2 a ofthe capacitive elements C1 and C2 (not shown) of the force sensor 800 cat a time when the force −Fz in the negative Z-axis direction acts onthe force receiving portion 814 are expressed by [Expression 31] shownbelow.C1a=C1+ΔCC2a=C2  [Expression 31]

Although not shown in the drawings, when a force +Fz in the positiveZ-axis direction acts on the force sensor 800 c, on the other hand, thetilting portion 813 tilts clockwise, and, due to the action of theapplied force +Fz, the tilting portion 813 is pulled upward in thepositive Z-axis direction via the first deformable portion 811. As aresult, the tilting portion 813 is slightly displaced in the positiveZ-axis direction in total.

At the same time, due to the tilting movement of the tilting portion813, the beam 821 connected to the lower end of the tilting portion 813also tilts clockwise. As a result, the first displacement portion D1 ofthe beam 821 is displaced in a direction in which the distance to thesupport 850 increases, and the second displacement portion D2 isdisplaced in a direction in which the distance to the support 850decreases. Therefore, the displacement caused in the first displacementportion D1 when the force +Fz is applied is the sum of the overalldisplacement of the above described tilting portion 813 in the positiveZ-axis direction and the displacement in the positive Z-axis directiondue to the tilting movement of the beam 821, and the displacement causedin the second displacement portion D2 is the sum of the overalldisplacement of the tilting portion 813 in the positive Z-axis directionand the displacement in the negative Z-axis direction due to the tiltingmovement of the beam 821. In this embodiment, the length of theconnecting body 822 in the Z-axis direction and the distance from thelongitudinal direction 1 of the tilting portion 813 to the seconddisplacement portion D2 are in the above predetermined relationship.Accordingly, the distance between the second displacement electrode Em2and the second fixed electrode Ef2 does not actually change.

As described above, in the force sensor 800 c according to thisembodiment, the second displacement portion D2 is designed not to besubstantially displaced in the Z-axis direction when the tilting portion813 is displaced in its longitudinal direction 1. Thus, it is possibleto detect the applied force Fz in the Z-axis direction through a simplecalculation.

<8-2. Modification of the Force Sensor 200 c Shown in FIG. 18>

Next, a modification of the force sensor 200 c shown in FIG. 18 to whichthe configuration described in 8-1, is applied is described.

As described above, the force sensor 200 c shown in FIG. 18 is formedwith four basic structures 100 that are the same as the basic structure100 shown in FIG. 1 and are arranged in a ring-like form (see 2-1.).This modification is a force sensor 801 c formed by replacing each ofthe four basic structures 100 (first through fourth deformable elements210A through 210D) with the basic structure 800 described in 8-1.Therefore, the same names as the names used in describing the forcesensor 200 c are used for the components equivalent to the components ofthe force sensor 200 c shown in FIG. 18.

In a case where a force +Fx in the positive X-axis direction, a force+Fy in the positive Y-axis direction, and a moment around the positiveZ-axis act on the force sensor 801 c according to this modification, anyforce in the Z-axis direction does not act on the force receivingportions 814A through 814D of respective deformable elements 810Athrough 810D. Therefore, the changes in the capacitance values of thecapacitive elements C11 through C42 are as shown in the respectivecolumns for Fx, Fy, and Mz in the table shown in FIG. 20.

When a force +Fz in the positive Z-axis direction acts on the forcesensor 801 c, on the other hand, a force in the Z-axis direction acts onthe respective force receiving portions of the first through fourthdeformable elements 810A through 810D. Therefore, the displacement ofthe 1-2nd displacement portion D12 in the Z-axis direction is zero inthe first deformable element 810A, the displacement of the 2-1stdisplacement portion D21 in the Z-axis direction is zero in the seconddeformable element 810B, the displacement of the 3-2nd displacementportion D32 in the Z-axis direction is zero in the third deformableelement 810C, and the displacement of the 4-1st displacement portion D41in the Z-axis direction is zero in the fourth deformable element 810D.The same applies in cases where the force −Fz, in the negative Z-axisdirection acts on the force sensor 801 c. Further, the phenomenon thatthe displacements of the four displacement portions D12, D21, D32, andD41 in the Z-axis direction become zero as described above also occursin cases where a moment Mx around the X-axis and a moment My around theY-axis are applied. In view of the above results, the changes caused inthe capacitance values of the capacitive elements C11 through C42 whenforces and moments Fx through Mz act on the force sensor 801 c are shownin a list in FIG. 50.

In accordance with the changes in the capacitance values of therespective capacitive elements C11 through C42, the measuring unit 841of a detection circuit 840 measures the applied forces and momentsaccording to [Expression 32] shown below. [Expression 32] is anexpression formed by deleting C12, C21, C32, and C41 from Mx and My in[Expression 14].Fx=C11−C12+C21−C22−C31+C32−C41+C42Fy=C11−C12−C21+C22−C31+C32+C41−C42Fz=−C11+C12+C21−C22−C31+C32+C41−C42Mx=−C11−C22+C31+C42My=−C11+C22+C31−C42Mz=−C11+C12−C21+C22−C31+C32−C41+C42  [Expression 32]

It should be noted that Fz in [Expression 32] still has C12, C21, C32,and C41. This is a devise for eliminating the influence of temperaturechanges and in-phase noise by measuring Fz through difference detection.

Next, the other-axis sensitivity of the force sensor 801 c according tothis modification is described.

FIG. 51 is a table as a list showing the other-axis sensitivities of thesix components of forces and moments in the force sensor 801 c accordingto the modification shown FIG. 47. As can be seen from FIG. 51, in theforce sensor 801 c, the force Fx in the X-axis direction and the momentMy around the Y-axis affect each other, and the force Fy in the Y-axisdirection and the moment Mx around the X-axis affect each other.Therefore, the force sensor 801 c should be used as a sensor fordetecting the four components Fx, Fy, Fz, and Mz in an environment whereMx and My are not applied, or should be used as a sensor for detectingthe four components Fz, Mx, My, and Mz in an environment where Fx, andFy are not applied.

Alternatively, applied forces and moments can also be measured accordingto [Expression 33] shown below.Fx=−C12+C31+C32−C41Fy=−C12−C21+C32+C41Fz=−C11+C12+C21−C22−C31+C32+C41−C42Mx=−C11−C12−C21−C22+C31+C32+C41+C42My=−C11+C12−C21+C22+C31+C32−C41−C42Mz=−C11+C21−C21+C22−C31+C32−C41+C42  [Expression 33]

In [Expression 33], the expressions for Fx and Fy are expressionsfocusing on only one of the two displacement portions provided in eachbeam. Since any of the six components can be measured in accordance withdifferences, it is possible to obtain the applied forces and momentswithout being affected by changes in environmental temperature andin-phase noise.

Further, where the other-axis sensitivities of the forces in therespective axis directions and the moments Fx through Mz around therespective axes are calculated according to [Expression 33], the resultsare as shown in a list in FIG. 52. The other-axis sensitivities arevalues obtained by assigning the six components Fx through Mz in thetable shown in FIG. 51 to the respective right sides of the above[Expression 33]. Each capacitive element with the symbol “+” isrepresented by +1, each capacitive element with the symbol “−” isrepresented by −1, and each capacitive element with “0” is representedby 0. As shown in FIG. 52, the other-axis sensitivities are zero incases where any of the components Fx through Mz is detected.

According to this modification described above, the same effects asthose of the force sensor 200 c according to the second embodiment canbe achieved, and further, applied forces and moments can be detectedthrough simpler calculations.

<8-3. Modification of the Force Sensor 500 c Shown in FIG. 36>

Next, a modification of the force sensor 500 c shown in FIG. 36 to whichthe configuration described in 8-1. is applied is described.

As described above, the force sensor 500 c shown in FIG. 36 is formedwith eight basic structures 100 that are the same as the basic structure100 shown in FIG. 1 and are arranged in a rectangular closed-loop form(see 5-1). This modification is a force sensor 802 c formed by replacingeach of the eight basic structures 100 (first through eighth deformableelements 210A through 210H) with the basic structure 800 described in8-1. Here, the same names as the names used in describing the forcesensor 500 c are used for the components equivalent to the components ofthe force sensor 500 c shown in FIG. 36.

In a case where a force −Fx in the positive X-axis direction, a force+Fy in the positive Y-axis direction, and a moment around the positiveZ-axis act on the force sensor 802 c according to this modification, anyforce in the Z-axis direction does not act on the force receivingportions 814A through 814H of respective deformable elements 810Athrough 810H. Therefore, the changes in the capacitance values of thecapacitive elements C11 through C82 are as shown in the respectivecolumns for Fx, Fy, and Mz in the table shown in FIG. 38.

When a force −Fz in the positive Z-axis direction acts on the forcesensor 802 c, on the other hand, a force in the positive Z-axisdirection acts on the respective force receiving portions of the firstthrough eighth deformable elements 810A through 810H. Therefore, thedisplacement of the 1-2nd displacement portion D12 in the Z-axisdirection is zero in the first deformable element 810A, the displacementof the 2-1st displacement portion D21 in the Z-axis direction is zero inthe second deformable element 810B, the displacement of the 3-2nddisplacement portion D32 in the Z-axis direction is zero in the thirddeformable element 810C, the displacement of the 4-1st displacementportion D41 in the Z-axis direction is zero in the fourth deformableelement 810D, the displacement of the 5-2nd displacement portion D52 inthe Z-axis direction is zero in the fifth deformable element 810E, thedisplacement of the 6-1st displacement portion D61 in the Z-axisdirection is zero in the sixth deformable element 810F, the displacementof the 7-2nd displacement portion D72 in the Z-axis direction is zero inthe seventh deformable element 810G, and the displacement of the 8-1stdisplacement portion D81 in the Z-axis direction is zero in the eighthdeformable element 810H. The same applies in cases where the force −Fzin the negative Z-axis direction acts on the force sensor 802 c.Further, the phenomenon that the displacements of the eight displacementportions D12, D21, D32, D41, D52, D61, D72, and D81 in the Z-axisdirection become zero as described above also occurs in cases where amoment Mx around the X-axis and a moment My around the Y-axis areapplied. In view of the above results, the changes caused in thecapacitance values of the capacitive elements C11 through C82 whenforces and moments Fx through Mz act on the force sensor 802 c are shownin a list in FIG. 53.

In accordance with the changes in the capacitance values of therespective capacitive elements C11 through C82, the measuring unit 841of the detection circuit 840 measures the applied forces and momentsaccording to [Expression 34] shown below. [Expression 34] is based on[Expression 22] through [Expression 27], and is an expression obtainedby deleting C12, C21, C32, C41, C52, C61, C72, and C81 from theexpressions for Mx and My.+Fx=C21−C22+C31−C32−C61+C62−C71+C72+Fy=C11−C12−C41+C42−C51+C52+C81−C82+Fz=−C11+C12+C21−C22−C31+C32+C41−C42−C51+C52+C61−C62−C71+C72+C81−C82+Mx=−C22−C31+C62+C71+My=−C11+C42+C51−C82+Mz=−C11+C12−C21+C22−C31+C32−C41+C42−C51+C52−C61+C62−C71+C72C81+C82  [Expression34]

It should be noted that Fz in [Expression 34] still has C12, C21, C32,C41, C52, C61, C72, and C81. This is a devise for eliminating theinfluence of temperature changes and in-phase noise by measuring Fzthrough difference detection. Since any of the six components can bemeasured from differences according to [Expression 34], it is possibleto obtain the applied forces and moments without being affected bychanges in environmental temperature and in-phase noise.

Next, the other-axis sensitivity of the force sensor 802 c according tothis modification is described.

FIG. 54 is a table as a list showing the other-axis sensitivities of thesix components of forces and moments in the force sensor 802 ccorresponding to FIG. 53, The method of calculating other-axissensitivities is as described in 8-2. As shown in FIG. 54, in the forcesensor 802 c, the other-axis sensitivities are zero in cases where anyof the components Fx through Mz is detected.

According to this modification described above, the same effects asthose of the force sensor 500 c according to the fifth embodiment can beachieved, and further, applied forces and moments can be detectedthrough simpler calculations.

In [Expression 34], the six components Fx through Mz are calculated fromsixteen variables C11 through C82, and therefore, there is redundancy.To carry out more efficient measurement, capacitance analysis may beconducted through computer simulations, and six or more capacitiveelements may be selected from the sixteen capacitive elements. In thiscase, the influence of other-axis sensitivities can be eliminated byperforming the above described correcting operation.

§ 9. Modifications

<9-1. Modification of the Force Receiving Body>

In each of the force sensors 200 c through 802 c described in § 2through § 8, the deformable bodies and the force receiving body arealigned in the Z-axis direction (in the vertical direction in eachdrawing), as shown in FIGS. 9, 10, 19, 30, 37, and 41, and otherdrawings. However, the present invention is not limited to such a mode,

FIG. 55 is a schematic cross-sectional view of an example of the basicstructure 201 of a force sensor in which a force receiving body isdisposed on the outer circumferential side of a deformable body. Thestructure shown in FIG. 55 corresponds to a modification of the basicstructure 200 of the force sensor 200 c according to the secondembodiment. Therefore, in FIG. 55, in each of the force sensors 200 cthrough 802 c described above, the force receiving body main body 261 aof a force receiving body 260 a is formed in a shape similar to theshape of the contour of the outer circumference of a deformable body210, and may be positioned to surround the outer circumference of thedeformable body 210, as shown in FIG. 55. In this case, force receivingportion connecting bodies 262 a and 263 a that connect the forcereceiving body main body 261 a and the deformable body 210 are providedon the outer circumferential surface of the deformable body 210.

In this case, the deformable body 210 and the force receiving body 260 aare disposed in the same plane, and thus, the size of the force sensorin the Z-axis direction can be made smaller (thinner).

<9-2. Modification (1) of the Deformable Body>

FIG. 56 is a schematic side view of a modification of the force sensor100 c of § 1.

As shown in FIG. 56, a force sensor 100 ca according to thismodification differs from the force sensor 100 c according to the firstembodiment in the layout of a first deformable portion 11 a and a seconddeformable portion 12 a. Specifically, the first deformable portion 11and the tilting portion 13 are connected at the lower end portion (theend portion on the negative Z-axis side) of the tilting portion 13 inthe force sensor 100 c according to the first embodiment, but areconnected at the upper end portion (the end portion on the positiveZ-axis side) of the tilting portion 13 in this modification.Furthermore, the second deformable portion 12 and the tilting portion 13are connected at the upper end portion of the tilting portion 13 in theforce sensor 100 c according to the first embodiment, but a seconddeformable portion 12 c and the tilting portion 13 are connected at thelower end portion of the tilting portion 13 in this modification. Theother aspects are the same as those of the force sensor 100 c accordingto the first embodiment. In FIG. 56, the same components as those of theforce sensor 100 c are denoted by the same reference numerals as thoseused in the force sensor 100 c, and detailed explanation thereof is notmade herein.

In the force sensor 100 ca according to this modification, when a force+Fx in the positive X-axis direction (the rightward direction in FIG.56) acts on the force receiving portion 14, the tilting portion 13 tiltsclockwise, and, when a force −Fx in the negative X-axis direction (theleftward direction in FIG. 56) acts on the force receiving portion 14,the tilting portion 13 tilts counterclockwise. These tilting directionsare the opposite of those in the first embodiment. On the other hand,when a force +Fz in the positive Z-axis direction (the upward directionin FIG. 56) acts on the force receiving portion 14, the tilting portion13 tilts clockwise, and, when a force −Fz in the negative Z-axisdirection (the downward direction in FIG. 56) acts on the forcereceiving portion 14, the tilting portion 13 tilts counterclockwise.These tilting directions are the same as those in the first embodiment.

Therefore, to measure a force acting on the force receiving portion 14with the force sensor 100 ca according to this modification, the sign ofthe right side of [Expression 3] should be reversed in a case where aforce in the X-axis direction is to be detected, and [Expression 5]should be adopted without any change in a case where a force in theZ-axis direction is to be detected.

It should be understood that the above deformable portion 10 a is notonly used in the first embodiment, but may also be used in the forcesensors according to the respective embodiments and modificationsdescribed in § 2 through § 8. In this case, when a force in the X-axisdirection acts on the deformable portion 10 a, the signs of the changesin the capacitance values of the respective capacitive elementsdescribed in the embodiments and modifications in § 2 through § 8 shouldbe reversed.

<9-3, Modification (2) of the Deformable Body>

FIG. 57 is a schematic side view of a further modification of the forcesensor 100 c of § 1.

A force sensor 100 cb according to this modification differs from thefirst embodiment in the structure of the displacement body 20.Specifically, as shown in FIG. 57, a displacement body 20 b of the forcesensor 100 cb is connected not to the lower end of the tilting portion13 but to a middle portion 13 m between the upper end and the lower endof the tilting portion 13. In this case, the beam 21 exhibits behaviorssimilar to those in the force sensor 100 c according to the firstembodiment, and therefore, the method of measuring the forces Fx and Fzdescribed in § 1 can be adopted without any change.

It should be understood that the deformable portion 10 b of thismodification is not only used in the first embodiment, but may also beused in the force sensors according to the respective embodiments andmodifications described in § 2 through § 8.

<9-4. Modification (3) of the Deformable Body>

FIG. 58 is a schematic side view of a further modification of the forcesensor 101 cb shown in FIG. 57.

As shown in FIG. 58, in a force sensor 101 cc according to thismodification, a tilting portion 13 c is designed to be shorter than thetilting portions shown in FIGS. 1, 56, 57, and others, and in theinitial state, the longitudinal direction 1 thereof is at an acute angleto the Z-axis. Further, a first deformable portion 11 c of the forcesensor 101 cc includes: a 1-1st deformable portion 11 c 1 extendingparallel to the X-axis from the force receiving portion 14; and a 1-2nddeformable portion 11 c 2 that extends parallel to the longitudinaldirection 1 of the tilting portion 13 c from the tip of the 1-1stdeformable portion 11 c 1, and is joined to one of the end portions ofthe tilting portion 13 c. Meanwhile, a second deformable portion 12 c ofthe force sensor 101 cc includes: a 2-1st deformable portion 12 c 1extending parallel to the X-axis from the top end of the fixed portion15; and a 2-2nd deformable portion 12 c 2 that extends parallel to thelongitudinal direction 1 of the tilting portion 13 c from the tip of the2-1st deformable portion, and is joined to the other one of the endportions of the tilting portion 13 c. Further, the displacement body 20c includes: a connecting body 22 c that downwardly, extends parallel tothe Z-axis from the tilting portion 13 c; and a beam 21 c joined to thelower end of the connecting body 22 c.

As the beam 21 c behaves in the same manner as that of the force sensor100 c according to the first embodiment, it is possible to properlymeasure forces Fx and Fz with the force sensor 100 cc described above,using the method of measuring the forces Fx and Fz as described in § 1.It should be understood that the deformable portion 10 c of thismodification is not only used in the first embodiment, but may also beused in the force sensors according to the respective embodiments andmodifications described in § 2 through § 8.

Although no further examples will be described, in short, thedisplacement body should have a structure that tilts (rotates) whenforces in the Z-axis direction and the X-axis direction act on the forcereceiving portion in a situation where the fixed body is not displaced.

In the three modifications shown in FIGS. 56 through 58, each of the twodisplacement electrodes and two fixed electrodes is disposed on a singleinsulator (insulating layer). With this arrangement, insulators (such asglass epoxy substrates or ceramic substrates) can be made from a singlesubstrate, and accordingly, force sensor productivity can beadvantageously increased.

<9-5. Modification (4) of the Deformable Body>

Next, a further modification of the force sensor 200 c according to thesecond embodiment shown in FIG. 18 is described.

FIG. 59 is a schematic top view of a force sensor 202 c according to amodification of FIG. 18. For ease of explanation, the force receivingbody is not shown in this drawing, either.

As shown in FIG. 59, the force sensor 202 c differs from the forcesensor 200 c shown in FIG. 18 in that a deformable body 210 b has arectangular shape. The deformable body 210 b includes: two forcereceiving portions 218 b and 219 b symmetrically arranged with respectto the origin O on the X-axis; and two fixed portions 216 b and 217 bsymmetrically arranged with respect to the origin O on the Y-axis. Theforce receiving portions and the fixed portions that are adjacent to oneanother along a closed-loop path are connected by four linear deformableelements 210Ab through 210Db. Accordingly, the basic structure 202 ofthe force sensor 202 c has a rectangular shape, with the two forcereceiving portions 218 b and 219 b and the two fixed portions 216 b and217 b being located at the four vertices. The deformable elements 210Abthrough 210Db are disposed one by one on the four sides of therectangle.

The other aspects are substantially the same as those of the forcesensor 200 c shown in FIG. 18. Therefore, in FIG. 59, the componentscorresponding to those of the force sensor 200 c shown in FIG. 18 aredenoted by substantially the same reference numerals (accompanied by“b”) as those used in the force sensor 200 c, and detailed explanationthereof is not made herein.

In the force sensor 202 c described above, each of the deformableelements 210A through 210D of the force sensor 200 c shown in FIG. 18 isformed not in an arc-like shape but in a linear shape. Therefore, theelastic deformations caused in the respective deformable elements 210Abthrough 210Db when forces and moments act on the force sensor 202 cshown in FIG. 59 are substantially the same as those in the force sensor200 c shown in FIG. 18, That is, the capacitance values of therespective capacitive elements C11 through C41 of the force sensor 202 caccording to this modification change with respect to the applied forcesand moments as shown in FIG. 20.

Thus, with the force sensor 202 c according to this modificationdescribed above, it is also possible to achieve the same effects asthose of the force sensor 200 c shown in FIG. 18.

It should be noted that the modification of the force receiving bodydescribed in 9-1. can also be used in this modification. In that case, aforce receiving body designed to have a rectangular shape similar to thecontour of the outer circumference of the deformable body 210 b isdisposed on the outer circumference of the deformable body 210 b.

REFERENCE SIGNS LIST

-   10 Deformable body-   10 a, 10 b, 10 c Deformable portion-   11, 11 a, 11 c First deformable portion-   12, 12 a, 12 c Second deformable portion-   13, 13 c Tilting portion-   13 m Middle portion-   14 Force receiving portion-   15 Fixed portion-   20, 20 b, 20 c Displacement body-   21, 21 c Beam-   22, 22 c Connecting body-   40 Detection circuit-   41 Measuring unit-   50 Support-   100 Basic structure-   100 c, 100 ca, 100 cb, 100 cc, 101 cb, 101 cc Force sensor200Basic    structure-   200 c Force sensor-   201 Basic structure-   210 Annular deformable body-   210A to 210D Deformable element-   213A to 213D Tilting portion-   216, 217 Fixed portion-   218, 219 Force receiving portion-   220A to 220D Displacement body-   221A to 221D Beam-   222A to 222D Connecting body-   240 Detection circuit-   241 Measuring unit-   250 Support-   260, 260 a Force receiving body-   261, 261 a Force receiving body main body-   262, 262 a Force receiving portion connecting body-   263, 263 a Force receiving portion connecting body-   300 c, 301 c Force sensor-   310 Deformable body-   313A to 213D Tilting portion-   316, 317 Fixed portion-   318, 319 Force receiving portion-   321A to 321D Beam-   340 Detection circuit-   341 Measuring unit-   350 Fixed body-   360 Force receiving body-   400 c, 401 c Force sensor-   410 Deformable body-   411A to 411D Beam-   413A to 413D Tilting portion-   416, 417 Fixed portion-   418, 419 Force receiving portion-   421A to 421D Beam-   441 Measuring unit-   450 Fixed body-   460 Force receiving body-   500 Basic structure-   500 c Force sensor-   510 Rectangular deformable body-   510A to 510H Deformable element-   513A to 513H Tilting portion-   514A, 514B, 514D, 514F Force receiving portion-   515B, 515C, 515E, 515H Fixed portion-   520A to 520H Displacement body-   521A to 521H Beam-   522A to 522H Connecting body-   540 Detection circuit-   541 Measuring unit-   550 Support-   560 Force receiving body-   561 Force receiving body main body-   562 to 565 Force receiving portion connecting body-   600 c Force sensor-   614A, 614B, 614D, 614F Force receiving portion-   621A to 621H Beam-   622A to 622H Connecting body-   640 Detection circuit-   641 Measuring unit-   660 Force receiving body-   700 c, 701 c Force sensor-   710 Annular deformable body-   710A to 710H Deformable element-   713A to 713H Tilting portion-   714A, 714B, 714D, 714F Force receiving portion-   721A to 721H Beam-   722A to 722H Connecting body-   740 Detection circuit-   741 Measuring unit-   760 Force receiving body-   800 Basic structure-   800 c, 801 c, 802 c Force sensor-   810 Deformable body-   811 First deformable portion-   812 Second deformable portion-   813 Tilting portion-   814 Force receiving portion-   821 Beam-   822 Connecting body-   840 Detection circuit-   841 Measuring unit-   850 Support

The invention claimed is:
 1. A force sensor comprising: a deformablebody that includes a force receiving portion and a fixed portion, and iselastically deformed by a force acting on the force receiving portion; adisplacement body that is connected to the deformable body, and isdisplaced by elastic deformation caused in the deformable body; and adetection circuit that detects an applied force, in accordance with adisplacement caused in the displacement body, wherein the deformablebody includes: a tilting portion that has a longitudinal direction andis disposed between the force receiving portion and the fixed portion; afirst deformable portion formed in curved shape, the first deformableportion connecting the force receiving portion and the tilting portion;and a second deformable portion formed in curved shape, the seconddeformable portion connecting the fixed portion and the tilting portion,the first deformable portion is disposed on one side of the tiltingportion, the second deformable portion is disposed on the other side ofthe tilting portion, a connecting portion between the first deformableportion and the tilting portion, and a connecting portion between thesecond deformable portion and the tilting portion differ in position inthe longitudinal direction of the tilting portion, the displacement bodyincludes a displacement portion that is connected to the tilting portionand is at a distance from the fixed portion, the displacement portionbeing displaced by a tilting movement of the tilting portion, and thedetection circuit includes a capacitive element disposed at thedisplacement portion, and detects an applied force in accordance with achange in a capacitance value of the capacitive element.
 2. The forcesensor according to claim 1, wherein the displacement body includes abeam that extends in a predetermined direction.
 3. The force sensoraccording to claim 2, wherein the displacement portion of thedisplacement body includes a first displacement portion and a seconddisplacement portion defined at different positions from each other onthe beam, and the detection circuit includes a first capacitive elementdisposed at the first displacement portion and a second capacitiveelement disposed at the second displacement portion, and detects anapplied force in accordance with changes in capacitance values of therespective capacitive elements.
 4. The force sensor according to claim3, wherein the displacement body includes a connecting body thatconnects the tilting portion of the deformable body and the beam, andthe first displacement portion and the second displacement portion ofthe displacement body are disposed on the beam symmetrically withrespect to a connecting portion between the connecting body and thebeam.
 5. The force sensor according to claim 3, wherein, in thedisplacement body, a displacement caused in the tilting portion and adisplacement caused in one of the first displacement portion and thesecond displacement portion when a force in a particular direction actson the force receiving portion are in opposite directions from eachother and are of the same size, to prevent the one of the displacementportions from being displaced.
 6. The force sensor according to claim 3,further comprising a support that is disposed to face the beam of thedisplacement body, and does not move relative to the fixed portion,wherein the first capacitive element includes a first displacementelectrode disposed at the first displacement portion of the displacementbody, and a first fixed electrode disposed on the support to face thefirst displacement electrode, and the second capacitive element includesa second displacement electrode disposed at the second displacementportion of the displacement body, and a second fixed electrode disposedon the support to face the second displacement electrode.
 7. The forcesensor according to claim 6, wherein the first displacement electrodeand the second displacement electrode, or the first fixed electrode andthe second fixed electrode are formed with a common electrode.
 8. Theforce sensor according to claim 1, further comprising a support that isdisposed to face the displacement body, and does not move relative tothe fixed portion, wherein the capacitive element includes adisplacement electrode disposed at the displacement portion of thedisplacement body, and a fixed electrode disposed on the support to facethe displacement electrode.
 9. The force sensor according to claim 8,further comprising: a force receiving body that is connected to theforce receiving portion of the deformable body, and receives an appliedforce; and a fixed body connected to the fixed portion of the deformablebody, wherein the fixed body is connected to the support.
 10. The forcesensor according to claim 1, wherein the deformable body is disposed onan X-Y plane in an X-Y-Z three-dimensional coordinate system, thelongitudinal direction of the tilting portion is a directionintersecting with the Z-axis, the first deformable portion connects theforce receiving portion and one end portion of the tilting portion, andthe second deformable portion connects the fixed portion and the otherend portion of the tilting portion.